#include <iostream>
#include <iomanip>
#include <cstdlib>
#include <cmath>
#include <string>
using namespace std;

int main()
{
	double vl, vr, d, w; cin >> vl >> vr >> d >> w;

	double ddist = 0;
	long long ldist = 0;
	double l = 0, r = d;
	int limit = 0;
	while (l < r && limit < 1000000) {
		double cnt;
		if (w > 0) cnt = (r - l) / (w + vr);
		else cnt = (r - l) / (vl - w);
		double dist = cnt*abs(w);
		int idist = dist;
		ldist += idist;
		ddist += dist - idist;
		l += cnt*vl;
		r -= cnt*vr;
		w = -w;
		limit++;
	}
	int iddist = ddist;
	ldist += iddist;
	ddist -= iddist;
	string s = to_string(ldist);

	for (int i = 0; i < s.size() - 1; i++) {
		cout << s[i];
	}
	ddist += ldist % 10;
	cout << fixed << setprecision(7) << ddist << endl;

	return 0;
}