#include <bits/stdc++.h>

using namespace std;
typedef pair<int, int> PII;
const int INF = 0x3f3f3f3f;
const int N = 150010, M = N << 1;

int st[N];
int dis[N]; // 距离数组

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

int n, m;
int dijkstra() {
    memset(dis, 0x3f, sizeof dis);
    dis[1] = 0;
    priority_queue<PII, vector<PII>, greater<PII>> q; // 小顶堆
    q.push({0, 1});

    while (q.size()) {
        PII t = q.top();
        q.pop();
        int u = t.second;
        if (!st[u]) {
            st[u] = 1;
            for (int i = h[u]; ~i; i = ne[i]) {
                int v = e[i];
                if (dis[v] > dis[u] + w[i]) {
                    dis[v] = dis[u] + w[i];
                    q.push({dis[v], v});
                }
            }
        }
    }
    if (dis[n] == INF) return -1;
    return dis[n];
}
int main() {
    cin >> n >> m;
    memset(h, -1, sizeof h);
    while (m--) {
        int a, b, c;
        cin >> a >> b >> c;
        add(a, b, c);
    }
    printf("%d\n", dijkstra());
    return 0;
}