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%;"/>.
str = raw_input() ;
f = [int(s) for s in str.split() if s.isdigit()]

a = f[0] ;
b = f[1] ;
c = f[2] ;
d = f[3] ;

if c == d:
	print "0"
else: 
	print (a*1.0/b)/(1.0 - (1.0 - (a*1.0/b))*(1.0 - (c*1.0/d))) 

