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#include <bits/stdc++.h>
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using namespace std;
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#pragma region Dijkstra算法模板
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//正无穷
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const int INF = 0x3f3f3f3f;
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//声明数据的最大维度
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const int N = 100;
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int n, m;
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//初始数据
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int mapp[N][N];
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bool visited[N];
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//距离,就是从1号顶点到其余各个顶点的初始路程
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int dist[N];
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//与求最短路相比，增加一个path数组，来记录最短路的路径,先将path[i]=-1，之后每次找出最短路的点p后将path[j]=p,用path[j]=i表示从i到j最短路的路径
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int path[N];
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/**
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* 功能：迪杰斯特拉算法
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* 试题板子
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* @param v 计算哪个节点做为起始点到各节点的距离
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*/
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void Dijkstra(int v) {
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//初始化
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for (int i = 1; i <= n; i++) {
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dist[i] = mapp[v][i];
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visited[i] = 0;
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path[i] = -1;
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}
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visited[v] = 1;
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for (int i = 1; i <= n; i++) {
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int p, minn = INF;
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for (int j = 1; j <= n; j++) {
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if (!visited[j] && dist[j] < minn) {
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p = j;
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minn = dist[j];
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}
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}
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visited[p] = 1;
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for (int j = 1; j <= n; j++) {
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if (!visited[j] && dist[p] + mapp[p][j] < dist[j]) {
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dist[j] = dist[p] + mapp[p][j];
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path[j] = p;
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}
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}
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}
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return;
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}
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/**
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* 功能：输出路径
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* @param s 起点
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* @param n 节点数量
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*/
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void print(int s, int n) {
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stack<int> q;
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for (int i = 2; i <= n; i++) {
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int p = i;
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while (path[p] != -1) {
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q.push(p);
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p = path[p];
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}
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q.push(p);
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cout << s << "-->" << i << " ";
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cout << "dis" << ":" << dist[i] << " ";
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cout << s;
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while (!q.empty()) {
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cout << "-->" << q.top();
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q.pop();
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}
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cout << endl;
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}
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}
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#pragma endregion Dijkstra算法模板
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int main() {
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//输入+输出重定向
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freopen("../1410.txt", "r", stdin);
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//n:哨所数
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//m:通信线路数
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cin >> n >> m;
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//1、初始化二维数组，全部为一个非常大的数据
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for (int i = 0; i <= n; i++) {
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for (int j = 0; j <= n; j++) {
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mapp[i][j] = INF;
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}
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}
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//2、s表示路径的起点，t表示路径的终点，edge表示该路径的长度。
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int i, j, k;
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//录入路径
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while (m--) {
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cin >> i >> j >> k;
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//将权写入
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mapp[i][j] = k;
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mapp[j][i] = k; //反向写入，无向图
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}
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//3、调用核心算法: 源点（统一规定为v1）到所有其他各定点的最短路径长度。
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Dijkstra(1);
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//输出结果
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int maxTime = 0;
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for (int i = 2; i <= n; i++) {
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if (dist[i] > maxTime) maxTime = dist[i];
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}
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if (maxTime == INF) cout << "-1" << endl;
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else cout << maxTime << endl;
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//关闭文件
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fclose(stdin);
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return 0;
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}
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