#include<cstring>
#include<iostream>
#include<algorithm>

using namespace std;

const int N = 510;

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

int dijkstra() {
    memset(dist, 0x3f, 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;

        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() {
    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);
    }
    cout << dijkstra() << endl;
    return 0;
}