#include <iostream>
#include <fstream>
#include <list>
#include <vector>
#include <queue>
using namespace std;
ifstream fin("darb.in");
ofstream fout("darb.out");

int n, m;
vector <list<int> > graph;
vector <int> order;
vector <bool> viz;
vector <int> lvl;
int diameter, last;

void read(){
    fin >> n >> m;
    graph.resize(n + 1);
    viz.resize(n + 1);
    lvl.resize(n + 1);
    for(int i = 0; i < m; i++){
        int x, y;
        fin >> x >> y;
        graph[x].push_back(y);
        graph[y].push_back(x);
    }
}

void bfs(int start){
    queue <int> q;
    for(auto i : viz)
        i = 0;
    for(auto i : lvl)
        i = 0;
    q.push(start);
    viz[start] = 1;
    lvl[start] = 1;
    while(!q.empty()){
        int v = q.front();
        q.pop();
        for(auto u : graph[v])
            if(!viz[u]){
                viz[u] = true;
                lvl[u] = lvl[v] + 1;
                last = u;
                diameter = lvl[u];
                q.push(u);
            }
    }
}

bool testTree(){
    if(m >= n) return false;
    bfs(1);
    bfs(last);
    fout << diameter;
    return true;
}



int main() {
    read();
    testTree();
    return 0;
}