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

int main(){
    int a, b, x, y;
    double ans;
    cin >> a >> b >> x >> y;
    if((double)x / a > (double)y / b){
        ans = y + (double)y/b*a;
    }else{
        ans = x + (double)x/a*b;    
    }
    cout << fixed << setprecision(7) << ans << endl;
    return 0;
}