func_code_string: #include <bits/stdc++.h>   using namespace std;   vector<int> vec, ves;   int main() {     int n, m, f = 0, w = 0;     bool p = false, t = false;     cin >> n;     for (int i = 0; i < n; i++) {       cin >> m;       if (m == 0) t = true;       for (int j = 0; j < vec.size(); j++) {         p = false;         if (m == vec[j]) {           ves[j]++;           p = true;           break;         }       }       if (p == false) {         vec.push_back(m);         ves.push_back(1);       }     }     for (int i = 0; i < vec.size(); i++) {       if (vec[i] != 0 && ves[i] > 2) {         cout << -1;         return 0;       } else if (ves[i] == 2 && vec[i] != 0)         w++;     }     cout << w;     return 0;   }   