func_code_string: #include <bits/stdc++.h>   using namespace std;   int main(int argc, char const *argv[]) {     int n, x;     while (cin >> n) {       map<int, int> a;       for (int i = 0; i < n; i++) {         cin >> x;         if (x != 0) a[x]++;       }       int ans = 0, ans1 = 0, ans2 = 0;       for (map<int, int>::iterator it = a.begin(); it != a.end(); it++) {         if (it->second == 2)           ans++;         else if (it->second < 2)           ans1++;         else           ans2++;       }       if (ans2 == 0 && ans > 0)         cout << ans << endl;       else if (ans2 == 0 && ans == 0)         cout << 0 << endl;       else         cout << -1 << endl;     }     return 0;   }   