#include<bits/stdc++.h>
using namespace std;

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

    if(b*x>a*y) printf("%.6f\n",(double)(a+b)*y/b);
    else printf("%.6f\n",(double)(a+b)*x/a);

    return 0;
}