#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
using namespace std;
const int N = 510,INF = 0x3f3f3f3f;
int g[N][N];
int dist[N];
bool st[N];
int n, m;

int dijkstra()
{
    memset(dist, INF, sizeof dist);
    dist[1] = 0;

    for (int i = 0; i < n - 1; i ++ )
    {
        int t = -1;
        for (int j = 1; j <= n; j ++ )
            if (!st[j] && (t == -1 || dist[t] > dist[j]))
                t = j;

        for (int j = 1; j <= n; j ++ )
            dist[j] = min(dist[j], dist[t] + g[t][j]);

        st[t] = true;
    }

    if (dist[n] == 0x3f3f3f3f) return -1;
    return dist[n];
}

int main()
{
    cin>>n>>m;
    memset(g,INF,sizeof g);
    while(m --)
    {
        int a,b,c;
        scanf("%d%d%d", &a,&b,&c);
        g[a][b] = min(g[a][b],c);
    }

    cout<<dijkstra()<<endl;

    return 0;
}