#include <iostream>
#include <vector>
#include <fstream>
using namespace std;
ifstream fin("darb.in");
ofstream fout("darb.out");
vector <int> L[100001];
int i,j,t,p,u,v[100001],d[100001],c[100001],nod,ok1=1,n,m,x,y,ok,dmax,nodmax;
void bfs (int a)
{
 p=1;
 u=1;

 c[1]=a;
 for(i=1;i<=n;i++)
    {v[i]=0;
    d[i]=0;}
d[a]=1;
 dmax=1;
 v[a]=1;
 while(p<=u)
 {
     for(i=0;i<L[c[p]].size();i++)
     {
         nod=L[c[p]][i];
         if(v[nod]==0)
         {
             d[nod]=d[c[p]]+1;
             v[nod]=1;
             u++;
             c[u]=nod;
         }
     }

     p++;

 }

}
int main()
{
  ifstream fin("bipartit1.in");
  ofstream fout("bipartit1.out");
  fin>>n>>m;
  for(i=1;i<=n;i++)
  {
      fin>>x>>y;
      L[x].push_back(y);
      L[y].push_back(x);

  }
 bfs(1);
 bfs(c[u]);
 fout<<d[c[u]];
}