To

#include<bits/stdc++.h>
using namespace std;
ifstream in("dmax.in");
ofstream out("dmax.out");
int a[101][101],n,m,x,y,v[101],c[101];
inline void bfs(int r,int h)
{
    register int k,st=1,dr=1;
    v[r]=h,c[st]=r;
    while(st<=dr)
    {
        k=c[st];
        for(int i=1;i<=n;i++)
            if(!v[i] && a[k][i])
            	v[i]=v[k]+1,c[++dr]=i;
        st++;
    }
}
inline void citire()
{
    in>>n>>m;
    while(in>>x>>y)
    	a[x][y]=a[y][x]=1;
    bfs(1,0);
    out<<distance(v+1,max_element(v+1,v+n+1))+1;
}
int main()
{
    citire();
    return 0;
}