func_code_string: #include <bits/stdc++.h>   using namespace std;   int32_t main() {     ios_base::sync_with_stdio(false);     cin.tie(0);     cout.tie(0);     long long t;     cin >> t;     while (t--) {       long long a, b, c, d;       cin >> a >> b >> c >> d;       if (a > (b * c)) {         cout << (-1) << endl;         continue;       }       long long k = (a / (d * b));       cout << (a * (k + 1)) - (d * b * k * (k + 1) / 2) << endl;     }     return 0;   }   