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

const int N = 1e5 + 10;
int n, m;
int dist[N];
bool st[N];
int h[N], e[N], ne[N], w[N], idx;
typedef pair<int, int> PII; //存<与源点距离，编号>

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

int main() {
    memset(h, -1, sizeof h);
    memset(dist, 0x3f, sizeof dist);
    priority_queue<PII, vector<PII>, greater<PII>> heap;
    cin >> n >> m;
    for (int i = 0; i < m; i ++ ) {
        int a, b, c;
        cin >> a >> b >> c;
        add(a, b, c);
    }
    dist[1] = 0;
    heap.push({0, 1});

    while (heap.size()) {
        auto t = heap.top();
        heap.pop();
        int v = t.second, d = t.first; //v是当前点的编号，d是当前点距离起点的距离
        if (st[v]) continue;
        st[v] = true;

        for (int i = h[v]; i != -1; i = ne[i]) {
            int j = e[i];
            if (dist[j] > dist[v] + w[i]) {
                dist[j] = dist[v] + w[i];
                heap.push({dist[j], j});
            }
        }
    }

    if (dist[n] != 0x3f3f3f3f) cout << dist[n] << endl;
    else cout << -1 << endl;

    return 0;
}