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

int main() {
double A,B,X,Y;
cin>>A>>B>>X>>Y;


if(A*Y==B*X){
	printf("%.8f",X+Y);
}else if(A*Y<B*X){
	printf("%.8f",Y+A*Y/B);
}else if(A*Y>B*X){
	printf("%.8f",X+B*X/A);
}

}