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#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;
}