Further research on zombie thought processes yielded interesting results. As we know from the previous problem, the nervous system of a zombie consists of n brains and m brain connectors joining some pairs of brains together. It was observed that the intellectual abilities of a zombie depend mainly on the topology of its nervous system. More precisely, we define the distance between two brains u and v (1 ≤ u, v ≤ n) as the minimum number of brain connectors used when transmitting a thought between these two brains. The brain latency of a zombie is defined to be the maximum distance between any two of its brains. Researchers conjecture that the brain latency is the crucial parameter which determines how smart a given zombie is. Help them test this conjecture by writing a program to compute brain latencies of nervous systems.

In this problem you may assume that any nervous system given in the input is valid, i.e., it satisfies conditions (1) and (2) from the easy version.

Sample Input

4 3
1 2
1 3
1 4

2

5 4
1 2
2 3
3 4
3 5

 #include <iostream>

 #include <cstdio>

 #include <vector>

 using namespace std;

 vector<int> p[];

 int ans,far;

 void Dfs(int cur,int pre,int step)

 {

     if (step>ans)

     {

         ans=step;

         far=cur;

     }

     int i,j;

     for (i=;i<p[cur].size();i++)

     {

         int to = p[cur][i];

         if (to!=pre)//不回头

         {

             Dfs(to,cur,step+);

         }

     }

 }

 int main()

 {

     int n,m;

     while (scanf("%d%d",&n,&m)!=EOF)

     {

         int i;

         for (i=;i<=n;i++)

             p[i].clear();

         for (i=;i<=m;i++)

         {

             int a,b;

             scanf("%d%d",&a,&b);

             p[a].push_back(b);

             p[b].push_back(a);

         }

         ans=;

         Dfs(,,);

         ans=;

         Dfs(far,,);

         printf("%d\n",ans);

     }

     return ;

 }