#include <iostream>
#include <iomanip>
using namespace std;

int main()
{
    double a,b,x,y;
    cin >> a >> b >> x >> y;

    if(x * b > y * a)
        cout << fixed << setprecision(10) << y * a / b + y << endl;
    else
        cout << fixed << setprecision(10) << x * b / a + x << endl;

    return 0;
}