#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
using namespace std;
const long long INF = 1e9, MOD = INF + 7;
long long gcd(long long a, long long b) { return (b ? gcd(b, a % b) : a); }
long long power(long long a, long long b) {
  return (!b ? 1 : power(a, b / 2) * power(a, b / 2) * (b % 2 ? a : 1));
}
long long mod(long long a) { return (a % MOD + MOD) % MOD; }
const long long N = 3e5 + 20;
vector<long long> g[N];
void dfs(long long v, long long &mx, long long &last, long long p = 0,
         long long h = 0) {
  if (h > mx) mx = h, last = v;
  for (long long u : g[v])
    if (u != p) dfs(u, mx, last, v, h + 1);
}
int32_t main() {
  ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  long long n, m;
  cin >> n >> m;
  for (long long i = 0; i < m; i++) {
    long long v, u;
    cin >> v >> u;
    g[v].push_back(u);
    g[u].push_back(v);
  }
  long long a = 1, b = 1, mx = 0;
  dfs(a, mx, b);
  dfs(b, mx, a);
  cout << mx << "\n";
  return 0;
}
