#include <bits/stdc++.h>
using namespace std;
const int MAXN = 1e5 + 10;
int n, m;
vector<int> g[MAXN];
int max1[MAXN], max2[MAXN];
bool vis[MAXN];
void dfs(int v) {
  vis[v] = true;
  for (auto to : g[v]) {
    if (!vis[to]) {
      dfs(to);
      if (max1[v] <= max1[to] + 1) {
        max2[v] = max1[v];
        max1[v] = max1[to] + 1;
      } else if (max2[v] < max1[to] + 1) {
        max2[v] = max1[to] + 1;
      }
    }
  }
}
int ans;
int main() {
  cin >> n >> m;
  while (m--) {
    int u, v;
    cin >> u >> v;
    g[u].push_back(v);
    g[v].push_back(u);
  }
  for (int i = 1; i <= n; i++)
    if (!vis[i]) dfs(i);
  for (int i = 1; i <= n; i++) ans = max(ans, max1[i] + max2[i]);
  cout << ans;
  return 0;
}
