#include <iostream>
#include <stdio.h>
using namespace std;
int main(int argc, char* argv[])
{
	int A,B,X,Y;
	cin>>A>>B>>X>>Y;
	double x1=(double)A/B;
	double x2=(double)X/double(Y);
	if (x1<x2){
		swap(A,B);
		swap(X,Y);
	}
	double aw=(double)X+(double)B*(double)X/double(A);
	if (aw==(int)aw){
		cout<<aw<<endl;
	}else{
		printf("%.12f",aw);
	}
	return 0;
}