1 #include<cstdio>
 2 #include<queue>
 3 #include<algorithm>
 4 #include<cstring>
 5 
 6 using namespace std;
 7 
 8 const int MAXN = 10010;
 9 
10 struct Edge{
11     int to,w,nxt;
12     Edge(){}
13     Edge(int x,int y,int z){to = x,w = y,nxt = z;}
14 }e[500100];
15 
16 int head[MAXN<<1],dis[MAXN];
17 int tot;
18 queue<int>q;
19 
20 int bfs(int x)
21 {
22     memset(dis,-1,sizeof(dis));
23     q.push(x);
24     dis[x] = 0;
25     int id,mx = 0;
26     
27     while (!q.empty())
28     {
29         int u = q.front();
30         q.pop();
31         for (int i=head[u]; i; i=e[i].nxt)
32         {
33             int v = e[i].to, w = e[i].w;
34             if (dis[v]==-1)    //双向边，只算一次 
35             {
36                 dis[v] = dis[u]+w;
37                 if (dis[v]>mx) mx = dis[v],id = v;
38                 q.push(v);
39             }
40         }
41     }
42     return id;
43 }
44 int main()
45 {
46     int u,v,w;
47     while (scanf("%d%d%d",&u,&v,&w)!=EOF)
48     {
49         e[++tot] = Edge(v,w,head[u]);
50         head[u] = tot;
51         e[++tot] = Edge(u,w,head[v]);
52         head[v] = tot;
53     }
54     printf("%d",dis[bfs(bfs(1))]);    
55     return 0;
56 }