#include <bits/stdc++.h>

using namespace std;

// AcWing 1128 信使【最短路】
// https://blog.csdn.net/qq_43964401/article/details/109039446


const int N = 110;
int n, m;
int d[N][N];

#define INF 0x3f3f3f3f

//floyd核心算法
void floyd() {
    for (int k = 1; k <= n; k++)
        for (int i = 1; i <= n; i++)
            for (int j = 1; j <= n; j++)
                d[i][j] = min(d[i][j], d[i][k] + d[k][j]);
}

int main() {
    //输入+输出重定向
    freopen("../1410.txt", "r", stdin);

    cin >> n >> m;

    //初始化
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= n; j++)
            if (i == j) d[i][j] = 0;
            else d[i][j] = INF;

    //输入数据
    while (m--) {
        int a, b, c;
        cin >> a >> b >> c;
        d[a][b] = c, d[b][a] = c; //双向，无向图
    }
    //核心计算
    floyd();

    //哪条路线最长
    int res = 0;
    for (int i = 1; i <= n; i++)
        res = max(res, d[1][i]);

    //如果有不存在的，就返回-1
    if (res >= INF) puts("-1");
    else printf("%d\n", res);

    //关闭文件
    fclose(stdin);
    return 0;
}