#include <bits/stdc++.h>
using namespace std;
int n, m, a, b, mx = 0;
vector <int> x[100500];
bool pr[100500];
int dfs(int v, int ans){
  pr[v] = 1;
  for(int i = 0; i < x[v].size(); i++){
    int d = ans;
    if(!pr[x[v][i]]){
      d++;
      mx = max(mx, d);
      dfs(x[v][i], d);
    }
  }
  return mx;
}
int main(){
  cin >> n >> m;
  for(int i = 0; i < m; i++){
    cin >> a >> b;
    x[a].push_back(b);
    x[b].push_back(a);
  }
  cout << dfs(1, 0);
  return 0;
}