#include <bits/stdc++.h>
using namespace std;
#define ll long long
int tt, tc;

const long double PI = acos(-1);

void solve() {
	long double h, r, da, dw;
	cin >> h >> r >> da >> dw;

	auto cyl = [&](long double height) {
		return PI * r * r * height;
	};

	long double totvol = cyl(h);

	auto f = [&](long double hw) {  // outputs the height of the center of mass
		long double volw = cyl(hw);
		long double massw = dw * volw;
		long double massa = da * (totvol - volw);
		long double h1 = hw / 2.0;
		long double h2 = hw + (h - hw) / 2.0;
		long double resh = massw * h1 + massa * h2;
		resh = resh / (massw + massa);
		return resh;
	};

	long double L = 0, R = h;
	int ctr = 100;
	while (ctr--) {
		long double mid = (R - L) / 3.0;
		long double y1 = L + mid, y2 = R - mid;
		if (f(y1) > f(y2)) L = y1;
		else R = y2;
	}
	cout << fixed << setprecision(9) << L << "\n";
}

int main() {
	ios::sync_with_stdio(0); cin.tie(0);
	tt = 1, tc = 1; //cin >> tt;
	while (tt--) solve(), tc++;
}