#include<bits/stdc++.h>
using namespace std;
int main(){
	int x,a,y,b,q,p;
	double z;
	cin>>x>>a>>y>>b;
	q=x*a;
	p=y*b;
	if(q>p){
		if(a>b){
			z=(q-p)/(a-b);
			printf("%.2lf",z);
		}else{
			z=(q-p)/(a-b);
			printf("%.2lf",+z);
		}
	}else{
		if(a>b){
			z=(p-q)/(a-b);
			printf("%.2lf",z);
		}else{
			z=(p-q)/(b-a);
			printf("%.2lf",z);
		}
	}
	return 0;
}