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 <img align="middle" class="tex-formula" src="https://espresso.codeforces.com/a7487d7e62f90136b78ae3fbf0a008396f146e13.png" style="max-width: 100.0%;max-height: 100.0%;"/> for SmallR while <img align="middle" class="tex-formula" src="https://espresso.codeforces.com/c443c7703e51f03d0eece0b96b9e84e425878209.png" style="max-width: 100.0%;max-height: 100.0%;"/> for Zanoes. The one who shoots in the target first should be the winner.

Output the probability that SmallR will win the match.
A single line contains four integers <img align="middle" class="tex-formula" src="https://espresso.codeforces.com/488158367221f441ba94b9475c03436069df2a7e.png" style="max-width: 100.0%;max-height: 100.0%;"/>.
a, b, c, d = map(int, input().split())
s = a/b
z = c/d
"""
Probability of SmallR winning in the first round:
s
Probability of SmallR winning in the second round (probability of him missing the first (1-s) and Zanoes also missing the first (1-z)):
(1-s)(1-z)s
Probability of SmallR winning in the third round (similar to previous):
(1-s)^2(1-z)^2s

The probability that Small wins is the sum of these probabilities:
s + (1-s)(1-z)s + (1-s)^2(1-z)^2s

Here I used chatGPT to help solve the series
The formula for the sum of a finite geometric series is given by:
Sum = a / (1 - r)
In this case a = s e r = is the ratio between consecutive terms: (1-s)^2(1-z)^2s/(1-s)(1-z)s = (1-s)(1-z)
"""
print(s / (1 - (1-s)*(1-z)))

 		 		  			  	  		 	  			 	 			