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#include <iostream>
#include <vector>
#include <queue>
#include <limits>

using namespace std;

const int INF = numeric_limits<int>::max();

struct Edge {
    int to;     
    int time;  
};
struct Compare {
    bool operator()(const pair<int, int>& a, const pair<int, int>& b) {
        return a.second > b.second;
    }
};
int calculateMinTime(int n, const vector<vector<Edge>>& graph) {
    vector<int> dist(n + 1, INF);  
    priority_queue<pair<int, int>, vector<pair<int, int>>, Compare> pq;

    dist[1] = 0;  
    pq.push({1, 0});

    while (!pq.empty()) {
        int current = pq.top().first;
        int currentDist = pq.top().second;
        pq.pop();
        if (currentDist > dist[current]) continue;
        for (const Edge& edge : graph[current]) {
            int next = edge.to;
            int time = edge.time;
            if (dist[next] > dist[current] + time) {
                dist[next] = dist[current] + time;
                pq.push({next, dist[next]});
            }
        }
    }
    int maxTime = 0;
    for (int i = 1; i <= n; ++i) {
        if (dist[i] == INF) return -1; 
        maxTime = max(maxTime, dist[i]);
    }

    return maxTime;
}

int main() {
    int n, m;
    cin >> n >> m;

    vector<vector<Edge>> graph(n + 1); 

    for (int i = 0; i < m; ++i) {
        int u, v, k;
        cin >> u >> v >> k;
        graph[u].push_back({v, k});
        graph[v].push_back({u, k});
    }

    int result = calculateMinTime(n, graph);
    cout << result << endl;

    return 0;
}