#include <bits/stdc++.h>
#define N 100005
using namespace std;
ifstream read("darb.in");
ofstream write("darb.out");
int n,m;
vector <int> v[N];
queue <int> q;
int viz[N];
int capat;

int bfs(int s){
    q.push(s);
    viz[s]=1;
    int x;
    while(!q.empty()){
        x=q.front();
        for(auto i:v[x]){
            if(viz[i]==0){
                q.push(i);
                viz[i]=1;
            }
        }
        capat=x;
        q.pop();
    }
return capat;
}
int maxim=0;
int dist[N];
int bfs2(int s){
    for(int i=0;i<m;i++)
        viz[i]=0;
    q.push(s);
    viz[s]=1;
    int x;
    while(!q.empty()){
        x=q.front();
        for(auto i:v[x]){
            if(viz[i]==0){
                q.push(i);
                dist[i]=dist[x]+1;
                maxim=max(maxim,dist[i]);
                viz[i]=1;
            }
        }
        capat=x;
        q.pop();
    }
    return maxim;
}
int main(){
    int a,b;
    read>>n>>m;
for(int i=0;i<m;i++)
    {
        read>>a>>b;
        v[a].push_back(b);
        v[b].push_back(a);
    }
        write<<bfs2(bfs(1));
return 0;
}