func_code_string: #include <bits/stdc++.h>   using namespace std;   using namespace std;   vector<vector<int> > g;   vector<int> depth;   void dfs(int v, int d = 0) {     depth[v] = d;     for (int to : g[v]) {       if (depth[to] == -1) {         dfs(to, d + 1);       }     }   }   int main() {     int n, m;     cin >> n >> m;     g.resize(n);     for (int i = 0; i < m; ++i) {       int u, v;       cin >> u >> v;       --u, --v;       g[u].push_back(v);       g[v].push_back(u);     }     depth.assign(n, -1);     dfs(0);     int v = 0;     for (int i = 1; i < n; ++i) {       if (depth[i] > depth[v]) {         v = i;       }     }     depth.assign(n, -1);     dfs(v);     int ans = 0;     for (int i = 0; i < n; ++i) {       ans = max(ans, depth[i]);     }     cout << ans <<   n ;   }   