#include <iostream>
#include <algorithm>
#include <iomanip>

using namespace std;

int main(){
    int a, b, x, y;
    cin >> a >> b >> x >> y;
    if(x * b > y * a){
        cout << setprecision(13) << y + double(y) * a / b << endl;
    }else{
        cout << setprecision(13) << x + double(x) * b / a << endl;
    }
}