func_code_string: #include <bits/stdc++.h>   using namespace std;   vector<vector<int>> g;   vector<int> vis, d;   void dfs(int v, int c) {     d[v] = c;     vis[v] = true;     for (int u : g[v]) {       if (!vis[u]) dfs(u, c + 1);     }   }   void solve() {     int n, m;     cin >> n >> m;     g.resize(n + 1, vector<int>());     vis.resize(n + 1, false);     d.resize(n + 1, -1);     while (m--) {       int a, b;       cin >> a >> b;       g[a].push_back(b);       g[b].push_back(a);     }     dfs(1, 0);     int u = max_element(d.begin(), d.end()) - d.begin();     vis.clear();     vis.resize(n + 1, false);     dfs(u, 0);     cout << (*max_element(d.begin(), d.end())) <<   n ;   }   int main() {     ios::sync_with_stdio(false);     cin.tie(NULL);     int T = 1;     while (T--) {       solve();     }   }   