import java.util.Arrays;
import java.util.LinkedList;
import java.util.Scanner;

public class Main {
	
	public static long MOD = 1000000007;
	
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		final double vl = sc.nextDouble();
		final double vr = sc.nextDouble();
		
		double d = sc.nextDouble();
		final double w = sc.nextDouble();
		
		double prev_answer = 0, answer = 0;
		while(true){
			final double go_right_t = d / (w + vr);
			answer += w * go_right_t;
			d -= go_right_t * (vl + vr);
			
			final double go_left_t = d / (w + vl);
			answer += w * go_left_t;
			d -= go_left_t * (vl + vr);
			
			if(Math.abs(prev_answer - answer) <= 1e-7){ break; }
			prev_answer = answer;
		}
		
		System.out.printf("%.8f\n", answer);
	}
}