func_code_string: #include <bits/stdc++.h>   using namespace std;   int i, j, k, l, m, n, x, y, z, ans, counting;   int ara[2000];   int main() {     cin >> n;     for (i = 0; i < n; i++) {       cin >> ara[i];     }     sort(ara, ara + n);     for (i = 0; i < n; i++) {       if (ara[i] != 0) break;     }     for (j = i + 1, counting = 1; j < n; j++) {       if (ara[j] == ara[j - 1]) {         counting++;       } else {         counting = 1;       }       if (counting > 2) {         printf( -1 );         return 0;       } else if (counting == 2)         ans++;     }     cout << ans;     return 0;   }   