func_code_string: #include <bits/stdc++.h>   using namespace std;   long long t, a, b, c, d;   signed main() {     ios::sync_with_stdio(false);     cin.tie(0);     cin >> t;     while (t--) {       cin >> a >> b >> c >> d;       long long l = 0, r = (c + d - 1) / d;       while (l < r) {         long long mid = l + r + 1 >> 1;         long long sum1 = (mid + 1) * mid / 2 * d * b - (mid + 1) * a;         if (mid == (c + d - 1) / d) sum1 -= (mid * d - c) * b;         long long sum2 = (mid - 1) * mid / 2 * d * b - mid * a;         if (sum1 >= sum2)           r = mid - 1;         else           l = mid;       }       if (l == (c + d - 1) / d)         cout <<  -1 n ;       else {         long long sum = (l + 1) * l / 2 * d * b - (l + 1) * a;         cout << -sum <<   n ;       }     }   }   