func_code_string: #include <bits/stdc++.h>   using namespace std;   int n;   long long A[100000 + 8], mark[20 + 8];   long long result = 0;   long long getC(int n, int k) {     if (n < k) return 0;     if (n == k) return 1;     long long result = 1;     for (long long i = max(k, n - k) + 1; i <= n; i++) result *= i;     return result / min(k, n - k);   }   int main() {     memset(mark, 0, sizeof mark);     cin >> n;     for (int i = 0; i < n; i++) {       cin >> A[i];       mark[A[i] + 10]++;     }     for (int i = 0; i <= 9; i++) result += mark[i] * mark[20 - i];     result += getC(mark[10], 2);     cout << result << endl;     return 0;   }   