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

using namespace std;

const int N = 510;

int g[N][N];
int n, m;
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 i = 1; i <= n; i ++)
        {
            if (!st[i] && (t == -1 || dist[i] < dist[t]))
                t = i;
        }

        st[t] = true;

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

    return dist[n];
}

int main()
{
    scanf("%d%d", &n, &m);

    memset(g, 0x3f, sizeof g);

    while (m --)
    {
        int a, b, c;
        scanf("%d%d%d", &a, &b, &c);
        g[a][b] = min(g[a][b], c);
    }

    int t = dijkstra();
    if (t == 0x3f3f3f3f) printf("-1");
    else printf("%d\n", t);

    return 0;
}