func_code_string: #include <bits/stdc++.h>   using namespace std;   const int maxn = 2 * 1000 * 100 + 100;   long long nums[maxn];   long long ans = 0;   long long cou[30];   int main() {     int n;     cin >> n;     for (int i = 0; i < n; i++) {       cin >> nums[i];       cou[nums[i] + 10]++;     }     ans += (cou[0 + 10] * (cou[10] - 1)) / 2;     for (int i = 1; i < 11; i++) {       ans += cou[i + 10] * cou[-i + 10];     }     cout << ans << endl;     return 0;   }   