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

int main(){
	double a, b, x, y;
	cin >> a >> b >> x >> y;
	double ans;
	if(a * y <= b * x){
		ans = y + (a * y) / b;
	}else{
		ans = x + (b * x) / a;
	}
	printf("%.10f\n", ans);
}