#include <bits/stdc++.h>
using namespace std;
#define double long double
double h,r,a,w;
double f(double i){
	double v = i/2*w*i + (h+i)*a/2*(h-i);
		v/=(i*w + (h-i)*a);
		return v; 
}
signed main(){
	cin.tie(nullptr)->sync_with_stdio(false);
	/*
	(m/2)*w + (h+m)r^2*a/2
	/m*w + (h-m)w


	*/
	
	cin >> h >> r >> a >> w;
	cout << fixed << setprecision(10);
	a = 1.0/a;
	w = 1.0/w;
	double low = 0;
	double high = h;
	double eps = 1e-7; //eps = 1/eps/eps;
	for(int iters = 0; iters<100; iters++){
		double i = (low+high)/2;
		if(f(i) < f(i+eps)){
			low = i;
		}
		else{
			high = i;
		}
	}
	cout << h-high << '\n';
	return 0;
}