import java.io.*;
import java.util.*;


public class Main_yukicoder450 {

	private static Scanner sc;
	private static Printer pr;

	private static void solve() {
		int vl = sc.nextInt();
		int vr = sc.nextInt();
		double d = sc.nextInt();
		int w = sc.nextInt();

		double ret = 0;
		for (int i = 0; i < 1000000 || d < 0; i++) {
			int v;
			if (i % 2 == 0) {
				v = vr + w;
			} else {
				v = vl + w;
			}

			double tmp = d / v;
			ret += tmp * w;
			d -= (vr + vl) * tmp;
		}

		pr.printf("%.7f\n", ret);

	}

	// ---------------------------------------------------
	public static void main(String[] args) {
		sc = new Scanner(System.in);
		pr = new Printer(System.out);

		solve();

		pr.close();
		sc.close();
	}

	private static class Printer extends PrintWriter {
		Printer(PrintStream out) {
			super(out);
		}
	}
}