#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;

const int N=510;
int n, m;
int g[N][N];
int dist[N];
bool st[N];

int dijkstra()
{
    memset(dist, 0x3f, sizeof dist);
    dist[1]=0;

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

        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()
{
    scanf("%d%d", &n, &m);
    memset(g, 0x3f, sizeof g);
    for (int i=0; i<m; i++) {
        int a, b, c;
        scanf("%d%d%d", &a, &b, &c);
        g[a][b]=min(g[a][b], c);
    }

    int res=dijkstra();
    printf("%d\n", res);
}