#include<iostream>
#include<vector>
#include<algorithm>
#include<string>
#include<cstdio>
using namespace std;
int main(){
    long long A,B,X,Y;
    cin >> A >> B >> X >> Y;
    if(X*B < Y*A) printf("%.8f",(double)X*(A+B)/A);
    else    printf("%.8f",(double)Y*(A+B)/B);
    return 0;
}