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

long double h, r, A, W;
long double calc(long double x) {
	long double n1 = x * x * W + (h * h - x * x) * A;
	long double n2 = x * W + (h - x) * A;
	return n1 / n2;
}

int main() {
	scanf("%Lf%Lf%Lf%Lf", &h, &r, &A, &W);
	long double l = 0, r = h;
	for (int i = 1; i <= 1000; ++i) {
		long double m1 = (l + l + r) / 3;
		long double m2 = (l + r + r) / 3;
		if (calc(m1) > calc(m2)) l = m1;
		else r = m2;
		//printf("%.12Lf %.12Lf\n", l, r);
	}
	printf("%.12Lf\n", l);
	return 0;
}