#include<cstring>
#include<iostream>
#include<algorithm>
#include<cstdio>using namespace std;const int N = 510;int g[N][N];//稠密用邻接矩阵存储int dist[N];//存储每个点到1号点的最短距离bool st[N];//判断每个点到1号点的最短距离是否确定int n, m;int dijkstra()
{memset(dist, 0x3f, sizeof dist);dist[1] = 0;for(int i = 0; i < n; i ++){int t = -1;//找出最短距离已经确定的点for(int j = 1; j <= n; j ++){if(!st[j] && (t == -1 || dist[t] > dist[j]))t = j;}st[t] = true;//用当前确定最短距离的点来更新其它点的距离for(int j = 1; j <= n; j ++){dist[j] = min(dist[j], dist[t] + g[t][j]);}}if(dist[n] == 0x3f3f3f3f) return -1;return dist[n];
}int main()
{cin >> n >> m;memset(g, 0x3f,sizeof g);while(m --){int a, b, c;cin >> a >> b >> c;g[a][b] = min(g[a][b], c);//存储重边中距离最短的}cout << dijkstra();return 0;
}//来自acwing