1.素数

     <1>定义：  一个大于1的自然数，除了1和它本身外，不能被其他自然数整除，换句话说就是该数除了1和它本身以外不再有其他的因数;否则称为合数。

    <2>证明为素数：

         方法1：如果有至少一个数用n取余后为0，则表明n为合数；如果所有数都不能整除n，则n为素数，算法复杂度O（n）。

         方法2：sqrt（n），此时算法复杂度O（sqrt（n））。范围（2~sqrt（n））

   <3>代码实现

int isPrime(int n) {int i, sqrtn = sqrt(n + 1e-6);if (n <= 1) {return 0;}for (i = 2; i <= sqrtn; i++) {if (n % i == 0) {return 0;}}return 1;
}

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2.回文数

    <1>定义：如果一个数从左往右读与从右往左读是一样的，那么这个数是回文数。例如121，1441，656.

    <2>分析：如果将数字本身反转，然后将反转后的数字与原始数字进行比较，如果它们是相同的，那么这个数字就是回文。

   <3.>细节：

             首先，我们应该处理一些临界情况。所有负数都不可能是回文，例如：-123 不是回文，因为 - 不等于 3。所以我们可以对所有负数返回 false。除了 0 以外，所有个位是 0 的数字不可能是回文，因为最高位不等于 0。所以我们可以对所有大于 0 且个位是 0 的数字返回 false。

            其次，对于数字 4224，如果执行 4224 % 10，我们将得到最后一位数字 4，要得到倒数第二位数字，我们可以先通过除以 10 把最后一位数字从 4224 中移除，4224 / 10 = 422，再求出上一步结果除以 10 的余数，422 % 10 = 2，就可以得到倒数第二位数字。如果我们把最后一位数字乘以 10，再加上倒数第二位数字，4 * 10 + 2 = 42，就得到了我们想要的反转后的数字.

   <4>代码实现：

             

int isPalindrome(int x) {if (x == 0)    //判断为0return 1;if (x < 0)      //判断是否为负数return 0;long t = x, ret = 0;  //注意这里用long，int的话范围较小while (t) {             //即为当t！=0的时候ret = ret * 10 + t % 10; t /= 10;}return ret = x;         //返回 }

---

3.回文素数

   线性查找的方法打表

   代码如下

int primePalindrome(int N){int nums[2000] = {2, 3, 5, 7, 11, 101, 131, 151, 181, 191, 313, 353, 373, 383, 727, 757, 787, 797, 919, 929, 10301, 10501, 10601, 11311, 11411, 12421, 12721, 12821, 13331, 13831, 13931, 14341, 14741, 15451, 15551, 16061, 16361, 16561, 16661, 17471, 17971, 18181, 18481, 19391, 19891, 19991, 30103, 30203, 30403, 30703, 30803, 31013, 31513, 32323, 32423, 33533, 34543, 34843, 35053, 35153, 35353, 35753, 36263, 36563, 37273, 37573, 38083, 38183, 38783, 39293, 70207, 70507, 70607, 71317, 71917, 72227, 72727, 73037, 73237, 73637, 74047, 74747, 75557, 76367, 76667, 77377, 77477, 77977, 78487, 78787, 78887, 79397, 79697, 79997, 90709, 91019, 93139, 93239, 93739, 94049, 94349, 94649, 94849, 94949, 95959, 96269, 96469, 96769, 97379, 97579, 97879, 98389, 98689, 1003001, 1008001, 1022201, 1028201, 1035301, 1043401, 1055501, 1062601, 1065601, 1074701, 1082801, 1085801, 1092901, 1093901, 1114111, 1117111, 1120211, 1123211, 1126211, 1129211, 1134311, 1145411, 1150511, 1153511, 1160611, 1163611, 1175711, 1177711, 1178711, 1180811, 1183811, 1186811, 1190911, 1193911, 1196911, 1201021, 1208021, 1212121, 1215121, 1218121, 1221221, 1235321, 1242421, 1243421, 1245421, 1250521, 1253521, 1257521, 1262621, 1268621, 1273721, 1276721, 1278721, 1280821, 1281821, 1286821, 1287821, 1300031, 1303031, 1311131, 1317131, 1327231, 1328231, 1333331, 1335331, 1338331, 1343431, 1360631, 1362631, 1363631, 1371731, 1374731, 1390931, 1407041, 1409041, 1411141, 1412141, 1422241, 1437341, 1444441, 1447441, 1452541, 1456541, 1461641, 1463641, 1464641, 1469641, 1486841, 1489841, 1490941, 1496941, 1508051, 1513151, 1520251, 1532351, 1535351, 1542451, 1548451, 1550551, 1551551, 1556551, 1557551, 1565651, 1572751, 1579751, 1580851, 1583851, 1589851, 1594951, 1597951, 1598951, 1600061, 1609061, 1611161, 1616161, 1628261, 1630361, 1633361, 1640461, 1643461, 1646461, 1654561, 1657561, 1658561, 1660661, 1670761, 1684861, 1685861, 1688861, 1695961, 1703071, 1707071, 1712171, 1714171, 1730371, 1734371, 1737371, 1748471, 1755571, 1761671, 1764671, 1777771, 1793971, 1802081, 1805081, 1820281, 1823281, 1824281, 1826281, 1829281, 1831381, 1832381, 1842481, 1851581, 1853581, 1856581, 1865681, 1876781, 1878781, 1879781, 1880881, 1881881, 1883881, 1884881, 1895981, 1903091, 1908091, 1909091, 1917191, 1924291, 1930391, 1936391, 1941491, 1951591, 1952591, 1957591, 1958591, 1963691, 1968691, 1969691, 1970791, 1976791, 1981891, 1982891, 1984891, 1987891, 1988891, 1993991, 1995991, 1998991, 3001003, 3002003, 3007003, 3016103, 3026203, 3064603, 3065603, 3072703, 3073703, 3075703, 3083803, 3089803, 3091903, 3095903, 3103013, 3106013, 3127213, 3135313, 3140413, 3155513, 3158513, 3160613, 3166613, 3181813, 3187813, 3193913, 3196913, 3198913, 3211123, 3212123, 3218123, 3222223, 3223223, 3228223, 3233323, 3236323, 3241423, 3245423, 3252523, 3256523, 3258523, 3260623, 3267623, 3272723, 3283823, 3285823, 3286823, 3288823, 3291923, 3293923, 3304033, 3305033, 3307033, 3310133, 3315133, 3319133, 3321233, 3329233, 3331333, 3337333, 3343433, 3353533, 3362633, 3364633, 3365633, 3368633, 3380833, 3391933, 3392933, 3400043, 3411143, 3417143, 3424243, 3425243, 3427243, 3439343, 3441443, 3443443, 3444443, 3447443, 3449443, 3452543, 3460643, 3466643, 3470743, 3479743, 3485843, 3487843, 3503053, 3515153, 3517153, 3528253, 3541453, 3553553, 3558553, 3563653, 3569653, 3586853, 3589853, 3590953, 3591953, 3594953, 3601063, 3607063, 3618163, 3621263, 3627263, 3635363, 3643463, 3646463, 3670763, 3673763, 3680863, 3689863, 3698963, 3708073, 3709073, 3716173, 3717173, 3721273, 3722273, 3728273, 3732373, 3743473, 3746473, 3762673, 3763673, 3765673, 3768673, 3769673, 3773773, 3774773, 3781873, 3784873, 3792973, 3793973, 3799973, 3804083, 3806083, 3812183, 3814183, 3826283, 3829283, 3836383, 3842483, 3853583, 3858583, 3863683, 3864683, 3867683, 3869683, 3871783, 3878783, 3893983, 3899983, 3913193, 3916193, 3918193, 3924293, 3927293, 3931393, 3938393, 3942493, 3946493, 3948493, 3964693, 3970793, 3983893, 3991993, 3994993, 3997993, 3998993, 7014107, 7035307, 7036307, 7041407, 7046407, 7057507, 7065607, 7069607, 7073707, 7079707, 7082807, 7084807, 7087807, 7093907, 7096907, 7100017, 7114117, 7115117, 7118117, 7129217, 7134317, 7136317, 7141417, 7145417, 7155517, 7156517, 7158517, 7159517, 7177717, 7190917, 7194917, 7215127, 7226227, 7246427, 7249427, 7250527, 7256527, 7257527, 7261627, 7267627, 7276727, 7278727, 7291927, 7300037, 7302037, 7310137, 7314137, 7324237, 7327237, 7347437, 7352537, 7354537, 7362637, 7365637, 7381837, 7388837, 7392937, 7401047, 7403047, 7409047, 7415147, 7434347, 7436347, 7439347, 7452547, 7461647, 7466647, 7472747, 7475747, 7485847, 7486847, 7489847, 7493947, 7507057, 7508057, 7518157, 7519157, 7521257, 7527257, 7540457, 7562657, 7564657, 7576757, 7586857, 7592957, 7594957, 7600067, 7611167, 7619167, 7622267, 7630367, 7632367, 7644467, 7654567, 7662667, 7665667, 7666667, 7668667, 7669667, 7674767, 7681867, 7690967, 7693967, 7696967, 7715177, 7718177, 7722277, 7729277, 7733377, 7742477, 7747477, 7750577, 7758577, 7764677, 7772777, 7774777, 7778777, 7782877, 7783877, 7791977, 7794977, 7807087, 7819187, 7820287, 7821287, 7831387, 7832387, 7838387, 7843487, 7850587, 7856587, 7865687, 7867687, 7868687, 7873787, 7884887, 7891987, 7897987, 7913197, 7916197, 7930397, 7933397, 7935397, 7938397, 7941497, 7943497, 7949497, 7957597, 7958597, 7960697, 7977797, 7984897, 7985897, 7987897, 7996997, 9002009, 9015109, 9024209, 9037309, 9042409, 9043409, 9045409, 9046409, 9049409, 9067609, 9073709, 9076709, 9078709, 9091909, 9095909, 9103019, 9109019, 9110119, 9127219, 9128219, 9136319, 9149419, 9169619, 9173719, 9174719, 9179719, 9185819, 9196919, 9199919, 9200029, 9209029, 9212129, 9217129, 9222229, 9223229, 9230329, 9231329, 9255529, 9269629, 9271729, 9277729, 9280829, 9286829, 9289829, 9318139, 9320239, 9324239, 9329239, 9332339, 9338339, 9351539, 9357539, 9375739, 9384839, 9397939, 9400049, 9414149, 9419149, 9433349, 9439349, 9440449, 9446449, 9451549, 9470749, 9477749, 9492949, 9493949, 9495949, 9504059, 9514159, 9526259, 9529259, 9547459, 9556559, 9558559, 9561659, 9577759, 9583859, 9585859, 9586859, 9601069, 9602069, 9604069, 9610169, 9620269, 9624269, 9626269, 9632369, 9634369, 9645469, 9650569, 9657569, 9670769, 9686869, 9700079, 9709079, 9711179, 9714179, 9724279, 9727279, 9732379, 9733379, 9743479, 9749479, 9752579, 9754579, 9758579, 9762679, 9770779, 9776779, 9779779, 9781879, 9782879, 9787879, 9788879, 9795979, 9801089, 9807089, 9809089, 9817189, 9818189, 9820289, 9822289, 9836389, 9837389, 9845489, 9852589, 9871789, 9888889, 9889889, 9896989, 9902099, 9907099, 9908099, 9916199, 9918199, 9919199, 9921299, 9923299, 9926299, 9927299, 9931399, 9932399, 9935399, 9938399, 9957599, 9965699, 9978799, 9980899, 9981899, 9989899, 100030001, 100050001, 100060001, 100111001, 100131001, 100161001, 100404001, 100656001, 100707001, 100767001, 100888001, 100999001, 101030101, 101060101, 101141101, 101171101, 101282101, 101292101, 101343101, 101373101, 101414101, 101424101, 101474101, 101595101, 101616101, 101717101, 101777101, 101838101, 101898101, 101919101, 101949101, 101999101, 102040201, 102070201, 102202201, 102232201, 102272201, 102343201, 102383201, 102454201, 102484201, 102515201, 102676201, 102686201, 102707201, 102808201, 102838201, 103000301, 103060301, 103161301, 103212301, 103282301, 103303301, 103323301, 103333301, 103363301, 103464301, 103515301, 103575301, 103696301, 103777301, 103818301, 103828301, 103909301, 103939301, 104000401, 104030401, 104040401, 104111401, 104222401, 104282401, 104333401, 104585401, 104616401, 104787401, 104838401, 104919401, 104949401, 105121501, 105191501, 105202501, 105262501, 105272501, 105313501, 105323501, 105343501, 105575501, 105616501, 105656501, 105757501, 105818501, 105868501, 105929501, 106060601, 106111601, 106131601, 106191601, 106222601, 106272601, 106353601, 106444601, 106464601, 106545601, 106555601, 106717601, 106909601, 106929601, 107000701, 107070701, 107121701, 107232701, 107393701, 107414701, 107424701, 107595701, 107636701, 107646701, 107747701, 107757701, 107828701, 107858701, 107868701, 107888701, 107939701, 107949701, 108070801, 108101801, 108121801, 108151801, 108212801, 108323801, 108373801, 108383801, 108434801, 108464801, 108484801, 108494801, 108505801, 108565801, 108686801, 108707801, 108767801, 108838801, 108919801, 108959801, 109000901, 109101901, 109111901, 109161901, 109333901, 109404901, 109434901, 109444901, 109474901, 109575901, 109656901, 109747901, 109777901, 109797901, 109818901, 109909901, 109929901, 110111011, 110232011, 110252011, 110343011, 110424011, 110505011, 110565011, 110676011, 110747011, 110757011, 110909011, 110949011, 110999011, 111010111, 111020111, 111050111, 111070111, 111181111, 111191111, 111262111, 111272111, 111454111, 111484111, 111515111, 111616111, 111686111, 111757111, 111848111, 112030211, 112060211, 112111211, 112161211, 112171211, 112212211, 112434211, 112494211, 112545211, 112636211, 112878211, 112959211, 112969211, 112989211, 113030311, 113090311, 113111311, 113262311, 113282311, 113474311, 113535311, 113565311, 113616311, 113636311, 113888311, 113939311, 114040411, 114191411, 114232411, 114353411, 114383411, 114484411, 114494411, 114535411, 114727411, 114808411, 114818411, 114848411, 114878411, 114898411, 115000511, 115020511, 115060511, 115111511, 115141511, 115191511, 115212511, 115222511, 115404511, 115464511, 115545511, 115636511, 115737511, 115767511, 115797511, 115828511, 115959511, 116000611, 116010611, 116040611, 116424611, 116505611, 116646611, 116696611, 116757611, 116777611, 116828611, 116868611, 116919611, 117070711, 117101711, 117262711, 117272711, 117323711, 117484711, 117505711, 117515711, 117616711, 117686711, 117757711, 117767711, 117797711, 117818711, 117959711, 118252811, 118272811, 118414811, 118464811, 118525811, 118626811, 118686811, 118696811, 118717811, 118818811, 118848811, 118909811, 118959811, 119010911, 119171911, 119202911, 119343911, 119363911, 119454911, 119585911, 119595911, 119646911, 119676911, 119696911, 119717911, 119787911, 119868911, 119888911, 119969911, 120191021, 120242021, 120434021, 120454021, 120494021, 120535021, 120565021, 120646021, 120808021, 120868021, 120989021, 121080121, 121111121, 121131121, 121161121, 121272121, 121282121, 121393121, 121414121, 121555121, 121747121, 121818121, 121878121, 121939121, 121989121, 122040221, 122232221, 122262221, 122292221, 122333221, 122363221, 122373221, 122393221, 122444221, 122484221, 122535221, 122696221, 122787221, 122858221, 122919221, 123161321, 123292321, 123424321, 123484321, 123494321, 123575321, 123767321, 123838321, 123989321, 124000421, 124080421, 124101421, 124131421, 124252421, 124323421, 124333421, 124434421, 124515421, 124525421, 124626421, 124656421, 124717421, 124737421, 124959421, 124989421, 125000521, 125010521, 125232521, 125252521, 125292521, 125343521, 125474521, 125505521, 125565521, 125606521, 125616521, 125757521, 125838521, 125939521, 125979521, 125999521, 126101621, 126161621, 126181621, 126202621, 126212621, 126323621, 126424621, 126484621, 126535621, 126595621, 126616621, 126676621, 126686621, 126727621, 126737621, 126757621, 126878621, 127060721, 127090721, 127131721, 127212721, 127383721, 127494721, 127545721, 127636721, 127656721, 127686721, 127717721, 127747721, 127828721, 127909721, 127929721, 128070821, 128090821, 128121821, 128181821, 128202821, 128252821, 128262821, 128282821, 128444821, 128474821, 128525821, 128535821, 128595821, 128646821, 128747821, 128787821, 128868821, 128919821, 128939821, 129080921, 129202921, 129292921, 129323921, 129373921, 129484921, 129494921, 129535921, 129737921, 129919921, 129979921, 130020031, 130030031, 130060031, 130141031, 130171031, 130222031, 130333031, 130444031, 130464031, 130545031, 130555031, 130585031, 130606031, 130636031, 130717031, 130767031, 130818031, 130828031, 130858031, 130969031, 131030131, 131111131, 131121131, 131222131, 131252131, 131333131, 131555131, 131565131, 131585131, 131646131, 131676131, 131828131, 132010231, 132191231, 132464231, 132535231, 132595231, 132646231, 132676231, 132757231, 133020331, 133060331, 133111331, 133161331, 133252331, 133474331, 133494331, 133575331, 133686331, 133767331, 133818331, 133909331, 134090431, 134181431, 134232431, 134424431, 134505431, 134525431, 134535431, 134616431, 134757431, 134808431, 134858431, 134888431, 134909431, 134919431, 134979431, 135010531, 135040531, 135101531, 135121531, 135161531, 135262531, 135434531, 135494531, 135515531, 135626531, 135646531, 135707531, 135838531, 135868531, 135878531, 135929531, 135959531, 135979531, 136090631, 136171631, 136222631, 136252631, 136303631, 136363631, 136474631, 136545631, 136737631, 136797631, 136818631, 136909631, 136969631, 137030731, 137040731, 137060731, 137090731, 137151731, 137171731, 137232731, 137282731, 137333731, 137363731, 137424731, 137474731, 137606731, 137636731, 137696731, 137757731, 137808731, 137838731, 137939731, 137999731, 138040831, 138131831, 138242831, 138292831, 138313831, 138383831, 138454831, 138575831, 138616831, 138646831, 138757831, 138898831, 138959831, 138989831, 139131931, 139161931, 139222931, 139252931, 139282931, 139383931, 139474931, 139515931, 139606931, 139626931, 139717931, 139848931, 139959931, 139969931, 139999931, 140000041, 140030041, 140151041, 140303041, 140505041, 140565041, 140606041, 140777041, 140787041, 140828041, 140868041, 140898041, 141020141, 141070141, 141131141, 141151141, 141242141, 141262141, 141313141, 141343141, 141383141, 141484141, 141494141, 141575141, 141595141, 141616141, 141767141, 141787141, 141848141, 142000241, 142030241, 142080241, 142252241, 142272241, 142353241, 142363241, 142464241, 142545241, 142555241, 142686241, 142707241, 142797241, 142858241, 142888241, 143090341, 143181341, 143262341, 143303341, 143454341, 143474341, 143585341, 143636341, 143787341, 143828341, 143919341, 143969341, 144010441, 144020441, 144202441, 144212441, 144313441, 144353441, 144404441, 144434441, 144484441, 144505441, 144707441, 144757441, 144808441, 144818441, 144848441, 144878441, 144898441, 144979441, 144989441, 145020541, 145030541, 145090541, 145353541, 145363541, 145393541, 145464541, 145494541, 145575541, 145666541, 145767541, 146030641, 146040641, 146181641, 146222641, 146252641, 146313641, 146363641, 146505641, 146555641, 146565641, 146676641, 146858641, 146909641, 147191741, 147232741, 147242741, 147313741, 147343741, 147373741, 147434741, 147515741, 147565741, 147616741, 147686741, 147707741, 147757741, 147838741, 147929741, 148020841, 148060841, 148080841, 148414841, 148444841, 148525841, 148545841, 148585841, 148666841, 148686841, 148707841, 148818841, 148858841, 148888841, 148969841, 149000941, 149333941, 149343941, 149484941, 149535941, 149555941, 149616941, 149646941, 149696941, 149858941, 149888941, 149909941, 149919941, 149939941, 150070051, 150151051, 150181051, 150202051, 150272051, 150434051, 150494051, 150505051, 150626051, 150686051, 150727051, 150808051, 150818051, 150979051, 151080151, 151161151, 151212151, 151222151, 151282151, 151353151, 151545151, 151585151, 151656151, 151737151, 151777151, 151858151, 151878151, 151888151, 151959151, 151969151, 151999151, 152090251, 152111251, 152171251, 152181251, 152252251, 152363251, 152393251, 152454251, 152505251, 152565251, 152616251, 152646251, 152666251, 152696251, 152888251, 152939251, 153212351, 153272351, 153292351, 153313351, 153323351, 153404351, 153424351, 153454351, 153484351, 153494351, 153626351, 153808351, 153818351, 153838351, 153979351, 154030451, 154191451, 154252451, 154272451, 154303451, 154323451, 154383451, 154393451, 154474451, 154494451, 154555451, 154575451, 154989451, 155060551, 155141551, 155171551, 155292551, 155313551, 155333551, 155373551, 155424551, 155474551, 155535551, 155646551, 155666551, 155676551, 155808551, 155828551, 155868551, 156151651, 156262651, 156343651, 156424651, 156434651, 156494651, 156545651, 156595651, 156656651, 156707651, 156727651, 156757651, 156848651, 156878651, 156949651, 157090751, 157101751, 157161751, 157252751, 157393751, 157444751, 157555751, 157717751, 157878751, 157888751, 157939751, 157959751, 157989751, 158090851, 158111851, 158222851, 158252851, 158363851, 158474851, 158595851, 158676851, 158696851, 158747851, 158808851, 158858851, 158898851, 158909851, 159020951, 159040951, 159050951, 159121951, 159181951, 159191951, 159202951, 159232951, 159262951, 159292951, 159323951, 159404951, 159464951, 159565951, 159595951, 159646951, 159757951, 159808951, 159919951, 159929951, 159959951, 160020061, 160050061, 160080061, 160101061, 160131061, 160141061, 160161061, 160171061, 160393061, 160545061, 160696061, 160707061, 160717061, 160797061, 160878061, 161171161, 161282161, 161313161, 161363161, 161474161, 161484161, 161535161, 161585161, 161636161, 161787161, 161838161, 161969161, 162040261, 162232261, 162404261, 162464261, 162484261, 162565261, 162686261, 162707261, 162757261, 162898261, 162919261, 162949261, 162959261, 162979261, 162989261, 163101361, 163333361, 163434361, 163464361, 163474361, 163494361, 163515361, 163555361, 163606361, 163686361, 163696361, 163878361, 163959361, 164000461, 164070461, 164151461, 164292461, 164333461, 164454461, 164484461, 164585461, 164616461, 164696461, 164717461, 164727461, 164838461, 165101561, 165161561, 165191561, 165212561, 165343561, 165515561, 165535561, 165808561, 165878561, 165898561, 165919561, 165949561, 166000661, 166080661, 166171661, 166191661, 166404661, 166545661, 166555661, 166636661, 166686661, 166818661, 166828661, 166878661, 166888661, 166929661, 167000761, 167111761, 167262761, 167393761, 167454761, 167474761, 167484761, 167636761, 167646761, 167787761, 167888761, 167898761, 167979761, 168151861, 168191861, 168232861, 168404861, 168505861, 168515861, 168565861, 168818861, 168898861, 168929861, 168949861, 169060961, 169131961, 169141961, 169282961, 169333961, 169383961, 169464961, 169555961, 169606961, 169656961, 169666961, 169686961, 169777961, 169797961, 169858961, 169999961, 170040071, 170060071, 170232071, 170303071, 170333071, 170414071, 170424071, 170484071, 170606071, 170616071, 170646071, 170828071, 170838071, 170909071, 170979071, 171080171, 171262171, 171292171, 171343171, 171565171, 171575171, 171767171, 171919171, 171959171, 172060271, 172090271, 172161271, 172353271, 172363271, 172393271, 172474271, 172585271, 172656271, 172747271, 172767271, 172797271, 172878271, 172909271, 172959271, 173000371, 173030371, 173090371, 173252371, 173373371, 173454371, 173525371, 173585371, 173696371, 173757371, 173777371, 173828371, 173868371, 173888371, 173898371, 173919371, 174080471, 174121471, 174131471, 174181471, 174313471, 174343471, 174595471, 174646471, 174676471, 174919471, 174949471, 174979471, 174989471, 175000571, 175090571, 175101571, 175111571, 175353571, 175444571, 175555571, 175626571, 175747571, 175777571, 175848571, 175909571, 176090671, 176111671, 176141671, 176181671, 176232671, 176313671, 176333671, 176373671, 176393671, 176414671, 176585671, 176636671, 176646671, 176666671, 176696671, 176757671, 176787671, 176888671, 176898671, 176939671, 177121771, 177161771, 177202771, 177242771, 177323771, 177565771, 177616771, 177707771, 177757771, 177868771, 178101871, 178131871, 178141871, 178161871, 178353871, 178414871, 178515871, 178525871, 178656871, 178717871, 178747871, 178878871, 178969871, 178989871, 178999871, 179010971, 179060971, 179222971, 179232971, 179262971, 179414971, 179454971, 179484971, 179717971, 179777971, 179808971, 179858971, 179868971, 179909971, 179969971, 179999971, 180070081, 180101081, 180161081, 180292081, 180515081, 180535081, 180545081, 180565081, 180616081, 180757081, 180959081, 181111181, 181515181, 181545181, 181666181, 181737181, 181797181, 181888181, 182010281, 182202281, 182373281, 182585281, 182616281, 182636281, 182777281, 182858281, 182949281, 183232381, 183626381, 183656381, 183737381, 183898381, 183979381, 183989381, 184030481, 184212481, 184222481, 184303481, 184393481, 184414481, 184545481, 184585481, 184606481, 184636481, 184747481, 184818481, 184878481, 185232581, 185373581, 185393581, 185525581, 185555581, 185595581, 185676581, 185757581, 185838581, 185858581, 185868581, 185999581, 186010681, 186040681, 186050681, 186070681, 186101681, 186131681, 186151681, 186161681, 186424681, 186484681, 186505681, 186565681, 186656681, 186676681, 186787681, 186898681, 187090781, 187101781, 187111781, 187161781, 187272781, 187404781, 187434781, 187444781, 187525781, 187767781, 187909781, 187939781, 187999781, 188010881, 188060881, 188141881, 188151881, 188303881, 188373881, 188414881, 188454881, 188505881, 188525881, 188535881, 188616881, 188636881, 188646881, 188727881, 188777881, 188868881, 188888881, 188898881, 188979881, 189080981, 189131981, 189262981, 189292981, 189464981, 189535981, 189595981, 189727981, 189787981, 189838981, 189898981, 189929981, 190000091, 190020091, 190080091, 190101091, 190252091, 190404091, 190434091, 190464091, 190494091, 190656091, 190696091, 190717091, 190747091, 190777091, 190858091, 190909091, 191090191, 191171191, 191232191, 191292191, 191313191, 191565191, 191595191, 191727191, 191757191, 191838191, 191868191, 191939191, 191969191, 192101291, 192191291, 192202291, 192242291, 192313291, 192404291, 192454291, 192484291, 192767291, 192797291, 192898291, 193000391, 193030391, 193191391, 193212391, 193282391, 193303391, 193383391, 193414391, 193464391, 193555391, 193686391, 193858391, 193888391, 194000491, 194070491, 194121491, 194222491, 194232491, 194292491, 194303491, 194393491, 194505491, 194595491, 194606491, 194787491, 194939491, 194999491, 195010591, 195040591, 195070591, 195151591, 195202591, 195242591, 195353591, 195505591, 195545591, 195707591, 195767591, 195868591, 195878591, 195949591, 195979591, 196000691, 196090691, 196323691, 196333691, 196363691, 196696691, 196797691, 196828691, 196878691, 197030791, 197060791, 197070791, 197090791, 197111791, 197121791, 197202791, 197292791, 197343791, 197454791, 197525791, 197606791, 197616791, 197868791, 197898791, 197919791, 198040891, 198070891, 198080891, 198131891, 198292891, 198343891, 198353891, 198383891, 198454891, 198565891, 198656891, 198707891, 198787891, 198878891, 198919891, 199030991, 199080991, 199141991, 199171991, 199212991, 199242991, 199323991, 199353991, 199363991, 199393991, 199494991, 199515991, 199545991, 199656991, 199767991, 199909991, 199999991};for(int i=0;i<2000;i++){if(nums[i]>=N)  return nums[i];}return -1;
}