#include <iostream>
#include <fstream>
#include <vector>
#include <list>
#include <queue>
using namespace std;
ifstream fin("darb.in");
ofstream fout("darb.out");
int n,m;
vector <list <int> >L;
void Citire()
{
    int x,y;
    fin>>n>>m;
    L.resize(n+1);
    for(int i=1;i<=m;i++)
    {
        fin>>x>>y;
        L[x].push_back(y);
        L[y].push_back(x);
    }
}

vector<int> dist,viz;
int diametru, last;
void BFS(int x)
{
    queue <int> Q;
    for(int i=1;i<=n;i++) viz[i]=0;
    for(int i=1;i<=n;i++) dist[i]=0;
    Q.push(x); dist[x]=1; viz[x]=1;
    while(!Q.empty())
    {
        int v=Q.front();
        Q.pop();
        for(list <int> ::iterator it=L[v].begin(); it!=L[v].end(); it++)
            if(viz[*it]==0)
           {
            dist[*it]=dist[v]+1;
            viz[*it]=1;
            Q.push(*it);
            diametru=dist[*it];
            last=*it;
            }
    }
}
int main()
{
    Citire();
    dist.resize(n+1);
    viz.resize(n+1);
    BFS(1);
    BFS(last);

    fout<<diametru;
    return 0;
}