#include <iostream>
#include <vector>
#include <algorithm>

struct Edge {
    Edge(int dest, int we) {
        this->dest = dest;
        this->weight = we;
    }
    int dest, weight;
};

const int MAXN = 54321;
bool used[MAXN];
int count = 0, tin[MAXN], fup[MAXN];

void DfsBriges(int vertex, int parent, std::vector<std::vector<Edge>> &graph, int &answ) {
    used[vertex] = true;
    tin[vertex] = count;
    fup[vertex] = count++;
    for (Edge edge:graph[vertex]) {
        int dest = edge.dest;
        if (dest == parent) {
            continue;
        }
        if (used[dest]) {
            fup[vertex] = std::min(fup[vertex], fup[dest]);
        } else {
            DfsBriges(dest, vertex, graph, answ);
            fup[vertex] = std::min(fup[vertex], fup[dest]);
            if (fup[dest] > tin[vertex]) {
                answ = std::min(answ, edge.weight);
            }
        }
    }
}

int main() {
    int nn, mm;
    std::cin >> nn >> mm;
    std::vector<std::vector<Edge>> graph(nn + 1);
    for (int i = 0; i < mm; ++i) {
        int source, dest, weight;
        std::cin >> source >> dest >> weight;
        graph[source].push_back(Edge(dest, weight));
        graph[dest].push_back(Edge(source, weight));
    }
    int answ = 1e9;
    DfsBriges(1, -1, graph, answ);
    if (answ < 1e9) {
        std::cout << answ;
    } else {
        std::cout << -1;
    }
}