#include <stdio.h>
#include <math.h>

double px(double a1, double b1, double a2, double b2) {
	return (b2 - b1) / (a1 - a2);
}

double py(double a1, double b1, double a2, double b2) {
	return a1 * px(a1, b1, a2, b2) + b1;
}

int main() {
	double vl, vr, d, w;
	scanf("%lf %lf %lf %lf", &vl, &vr, &d, &w);

	double x1, y1, x2, y2, x3, y3;
	double tmp, ans = 0.0, tmpd;
	int flag = 0;

	x1 = y1 = 0;
	x2 = px(1 / w, 0, -(1 / vr), d / vr);
	y2 = py(1 / w, 0, -(1 / vr), d / vr);

	do {
		tmp = sqrt(pow(x2 - x1, 2) + pow(y2 - y1, 2));
		ans += tmp;

		if (flag) {
			x3 = px(-(1 / vr), d / vr, 1 / w, y2 - 1 / w * x2);
			y3 = py(-(1 / vr), d / vr, 1 / w, y2 - 1 / w * x2);
		}
		else {
			x3 = px(1 / vl, 0, -(1 / w), y2 + 1 / w * x2);
			y3 = py(1 / vl, 0, -(1 / w), y2 + 1 / w * x2);
		}

		x1 = x2; x2 = x3;
		y1 = y2; y2 = y3;
		tmpd = x2 - x1 > 0 ? x2 - x1 : x1 - x2;

		flag = !flag;
	}
	while (tmpd > 10e-8);

	printf("%.7lf\n", ans);
	return 0;
}