#include<bits/stdc++.h>
using namespace std;
typedef pair<int,int> PII;

const int N = 150010;


int h[N], e[N], w[N], ne[N], idx;
int n, m;
int dist[N];
int st[N];

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

int dijkstra() {
    memset(dist, 0x3f, sizeof dist);
    dist[1] = 0;
    priority_queue<PII,vector<PII>, greater<PII>> heap;
    heap.push({0, 1});
    st[1] = 1;
    while (heap.size()) {
        auto t = heap.top();
        heap.pop();
        int ver = t.second;
        int distance = t.first;
        // 如果ver已经更新过其他点了，就不用他再更新一遍了
        if (st[ver]) continue;
        st[ver] = 1;
        for (int i = h[ver]; i != -1; i = ne[i]) {
            int j = e[i];
            // 这里是用当前最短的源点去更新其他点
            if (dist[j] > distance + w[i]) {
                dist[j] = distance + w[i];
                // if (!st[j]) {
                    heap.push({dist[j], j});
                    // st[j] = 1;   
                    //这里是不对的，st的含义是更新过其他点的点，而这里的含义是被更新过的点
                // }

            }
        }
    }
    if (dist[n] == 0x3f3f3f3f) return -1;
    return dist[n];
}



int main() {
    cin >> n >> m;
    memset(h, -1, sizeof h);
    for (int i = 0; i < m; i++) {
        int a, b, c;
        cin >> a >> b >> c;
        add(a, b, c);
    }
    int t = dijkstra();
    // for (int i = 1; i <= n; i++) cout << dist[i] << endl;
    cout << t << endl;
    return 0;
}