#include <bits/stdc++.h>
using namespace std;

const int INF = 1e9;

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    int n, m;
    if (!(cin >> n >> m)) return 0;
    vector<vector<pair<int, int>>> adj(n + 1);
    for (int i = 0; i < m; i++) {
        int u, v, t;
        cin >> u >> v >> t;
        adj[u].push_back({v, t});
        adj[v].push_back({u, t});
    }
    vector<int> dist(n + 1, INF);
    deque<int> dq;
    dist[1] = 0;
    dq.push_back(1);
    while (!dq.empty()) {
        int u = dq.front();
        dq.pop_front();
        for (auto p : adj[u]) {
            int v = p.first;
            int w = p.second;
            if (dist[u] + w < dist[v]) {
                dist[v] = dist[u] + w;
                if (w == 0) {
                    dq.push_front(v);
                } else {
                    dq.push_back(v);
                }
            }
        }
    }
    if (dist[n] == INF) cout << -1 << "\n";
    else cout << dist[n] << "\n";
    return 0;
}