#include <iostream>
#include <cstring>

using namespace std;

const int N = 550, M = 100010;

int h[N], e[M], ne[M], w[M], idx;
int dist[N];
bool state[N];
int n, m;

void add(int a, int b, int c) {
    e[idx] = b, w[idx] = c, ne[idx] = h[a], h[a] = idx++;
}

void 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 (!state[j] && (t == -1 || (dist[j] < dist[t]))) {
                t = j;
            }
        }
        state[t] = true;
        for (int j = h[t]; j != -1; j = ne[j]) {
            int u = e[j];
            // printf("t:%d\n", t);
            // printf("dist[%d]:%d dist[t] + w[j]:%d\n", u, dist[u], dist[t] + w[j]);
            dist[u] = min(dist[u], dist[t] + w[j]);
            // printf("校正后:dist[%d] = %d\n", u, dist[u]);
        }
    }

}

int main(void)
{
    memset(h, -1, sizeof(h));
    cin >> n >> m;

    while (m--) {
        int a, b, w;
        cin >> a >> b >> w;
        add(a, b, w);
    }

    Dijkstra();

    // printf("n = %d\n", n);
    if (dist[n] != 0x3f3f3f3f) cout << dist[n] << endl;
    else cout << "-1" << endl;

    return 0;
}