func_code_string: #include <bits/stdc++.h>   using namespace std;   inline int max(int a, int b) { return a > b ? a : b; }   inline int min(int a, int b) { return a < b ? a : b; }   map<int, int> mp;   int main() {     int n, x;     cin >> n;     mp.clear();     for (int i(0); i < (n); ++i) {       cin >> x;       ++mp[x];     }     long long ans(0);     for (map<int, int>::iterator it = mp.begin(); it != mp.end() && it->first < 0;          ++it)       ans += (long long)it->second * (long long)mp[-it->first];     ans += (long long)mp[0] * ((long long)mp[0] - 1ll) / 2ll;     cout << ans << endl;     return 0;   }   