#include <iostream>
#include <vector>
#include <map>

using std::vector;

vector<int> graph[60000];
bool used[60000];
int timer, tin[60000], fup[60000];
long long answer = 1000000000000;
std::map<std::pair<int, int>, long long> costs;

void dfs(int vertex, int parent = -1) {
    used[vertex] = true;
    tin[vertex] = fup[vertex] = timer++;
    for (size_t i = 0; i < graph[vertex].size(); ++i) {
        int to = graph[vertex][i];
        if (to == parent) continue;
        if (used[to])
            fup[vertex] = std::min(fup[vertex], tin[to]);
        else {
            dfs(to, vertex);
            fup[vertex] = std::min(fup[vertex], fup[to]);
            if (fup[to] > tin[vertex]) {
                answer = std::min(answer, costs[std::make_pair(vertex, to)]);
            }
        }
    }
}

void find_bridges(int n_size) {
    timer = 0;
    for (int i = 0; i < n_size; ++i)
        used[i] = false;
    for (int i = 0; i < n_size; ++i)
        if (!used[i])
            dfs(i);
}

int main() {
    int n_size, m_size;
    std::cin >> n_size >> m_size;

    int a_city, b_city, cost;
    while (m_size--) {
        std::cin >> a_city >> b_city >> cost;
        graph[a_city - 1].push_back(b_city - 1);
        graph[b_city - 1].push_back(a_city - 1);
        costs[std::make_pair(a_city - 1, b_city - 1)] = cost;
        costs[std::make_pair(b_city - 1, a_city - 1)] = cost;

    }
    find_bridges(n_size);
    if (answer == 1000000000000) {
        answer = -1;
    }
    std::cout << answer;

    return 0;
}