func_code_string: #include <bits/stdc++.h>   using namespace std;   void blowback() {     long long i, j, l, k, n, m, x, y, r, ans = 0, sum = 10e17;     string s;     long long a, b, c, d;     cin >> a >> b >> c >> d;     if (a > (b * c)) {       cout <<  -1 n ;       return;     }     k = (2 * a - b * d) / (2 * b * d);     l = k + 1;     k = min(k, c / d);     l = min(l, c / d);     ans = (a * (k + 1)) - ((k * (k + 1)) * b * d) / 2;     k = l;     sum = (a * (k + 1)) - ((k * (k + 1)) * b * d) / 2;     cout << max({ans, sum, a}) <<   n ;   }   signed main() {     ios_base::sync_with_stdio(false);     cin.tie(0);     cout.tie(0);     long long int t = 1;     cin >> t;     while (t--) {       blowback();     }     return 0;   }   