#include <iostream>
#include <cstring>
#include <queue>

using namespace std;

const int N = 1000010;

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

typedef pair<int, int> PII; // dist, index

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>> q;
    q.push({0, 1});
    while (q.size()) {
        auto t = q.top();   // 找出距离源点最近的节点
        q.pop();
        int ver = t.second, distance = t.first;
        if (!state[ver]) state[ver] = true;
        else continue;
        for (int i = h[ver]; i != -1; i = ne[i]) {
            int j = e[i];
            if (dist[j] > distance + w[i]) {
                dist[j] = distance + w[i];
            }
            q.push({dist[j], j});
        }
    }
    if (dist[n] == 0x3f3f3f3f)  return -1;
    else return dist[n];
}

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

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

    cout << Dijkstra() << endl;

    return 0;
}