func_code_string: #include <bits/stdc++.h>   using namespace std;   const long long maxn = 1e6 + 10;   long long n, k, A[maxn];   int32_t main() {     ios_base::sync_with_stdio(false);     cin >> n;     for (long long i = 0; i < n; i++) {       long long a, b, c, d;       cin >> a >> b >> c >> d;       if (a > b * c) {         cout << -1 << endl;         continue;       }       long long e = (a + d * b - 1) / (d * b);       cout << e * a - (e * (e - 1ll) / 2ll * d * b) << endl;     }   }   