Problem: SmallR is an archer. SmallR is taking a match of archer with Zanoes. They try to shoot in the target in turns, and SmallR shoots first. The probability of shooting the target each time is <image> for SmallR while <image> for Zanoes. The one who shoots in the target first should be the winner.

Output the probability that SmallR will win the match.

Input

A single line contains four integers <image>.

Output

Print a single real number, the probability that SmallR will win the match.

The answer will be considered correct if the absolute or relative error doesn't exceed 10 - 6.

Examples

Input

1 2 1 2


Output

0.666666666667

Solution (in JAVA):

Solution:
import java.util.Scanner;


public class E {
	double EPS = 1e-9;
	public static void main(String[] args) {
		Scanner sc= new Scanner(System.in);
		double A = sc.nextInt();
		double B = sc.nextInt();
		double C = sc.nextInt();
		double D = sc.nextInt();
		double X = A/B;
		double Y = C/D;
		double ans = X*(1/(1-(((1-X)*(1-Y)))));
		System.out.println(ans);

	}

}