#include <iostream>
#include <sstream>
#include <algorithm>
#include <numeric>
#include <cstdio>

using namespace std;

int main(int argc, char *argv[]) {
	cout.precision(10);
	long double vl, vr, d, w, ans = 0, a = 999;
	cin >> vl >> vr >> d >> w;
	while (a > 1.0e-11 && d > 1.0e-11) {
		long double a = (d * w) / (w + vr), t = a / w;
		ans += a;
		d -= t * (vl + vr);
		a = (d * w) / (w + vl), t = a / w;
		ans += a;
		d -= t * (vl + vr);
	}
	cout << ans << endl;
	return 0;
}