func_code_string: #include <bits/stdc++.h>   using namespace std;   vector<set<int> > arr;   long long res = 0;   void dfs(int vertex, int prev, int level) {     for (int v : arr[vertex]) {       if (v == prev) {         continue;       }       if (level == 2) {         res++;         continue;       } else {         dfs(v, vertex, level + 1);       }     }   }   int main() {     ios::sync_with_stdio(0);     cin.tie(0);     int n;     cin >> n;     arr = vector<set<int> >(n + 1);     for (int i = 0; i < n; ++i) {       int a, b;       cin >> a >> b;       arr[a].insert(b);       arr[b].insert(a);     }     for (int i = 1; i <= n; ++i) {       dfs(i, -1, 1);     }     cout << res / 2 << endl;     return 0;   }   