#include <bits/stdc++.h> using namespace std; const int maxn = 1e5 + 1; vector <int> adj[maxn]; bool vis[maxn]; int node = 0, max_dis = -1; void dfs(int s, int p, int d) { if (d > max_dis) { node = s; max_dis = d; } vis[s] = true; for (auto i : adj[s]) { if (i == p) continue; dfs(i, s, d+1); } } int main() { int n, m; cin >> n >> m; for (int i = 0; i < m; i++) { int a, b; cin >> a >> b; adj[a].push_back(b); adj[b].push_back(a); } vector <pair <int, int>> endpoints; for (int i = 1; i <= n; i++) { if (vis[i]) continue; max_dis = -1; endpoints.emplace_back(); dfs(i, i, 0); endpoints.back().first = node; max_dis = -1; dfs(node, node, 0); endpoints.back().second = node; } for (int i = 0; i + 1 < (int)endpoints.size(); i++) { int a = endpoints[i].second, b = endpoints[i+1].first; adj[a].push_back(b); adj[b].push_back(a); } max_dis = -1; dfs(endpoints.back().second, 0, 0); cout << max_dis+1 << '\n'; }