#include <bits/stdc++.h>
using namespace std;
vector<int>pont[1500];
int el[1500],maxi=0;
void mely(int n){
    for(auto& i:pont[n]){
        if(el[i]==-1){
            el[i]=el[n]+1;
            mely(i);}
        else if(el[i]-el[n]>1){
            maxi=max(maxi, el[i]-el[n]+1);}}}
int main()
{
    int n,m,x,y;
    cin>>n>>m;
    fill(el,el+1500,-1);
    for(int i=0; i<m; i++){cin>>x>>y;
        pont[x-1].push_back(y-1);
        pont[y-1].push_back(x-1);}
    el[0]=0; mely(0);
    cout<<maxi;
    return 0;
}