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.*;
public class Test{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
         int b = sc.nextInt();
         int c = sc.nextInt();
          int d = sc.nextInt();
          double p = (double) a/b;
          
          double z = (double) c/d;
          double q = (double)((1 -p)*(1 -z));
          
          double ans = p/(1 - q);
          System.out.println(ans);
       
        
       
    }
}