1793A - Yet Another Promotion - CodeForces Solution

#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
using namespace std;

int main() {
    long long h,t,a,b,n,m,sum = 0;
    cin >> t;
    for (int i = 0; i < t; i++) {
        cin >> a >> b >> n >> m;
        sum = 0;
        h = n / (m + 1);
        n -= h * (m + 1);
        if (m * a < b * (m + 1))
           sum += (m * a)*h;
        else
            sum += (b * (m + 1))*h;
        if (a * n < b * n)
            sum += a * n;
        else
            sum += b * n;
        cout << sum << endl;
    }
    return 0;
}