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 = (int(x) for x in input().split())

# prob to win on 1st round
P_s = a / b
P_z = c / d

# prob to win on i-th round:
# prob_fail = 1 - prob_win_s
# prob_fail_i_round = prob_fail_s^i * prob_fail_z^i
# prob_1st_round * prob_fail_i-1_rounds

# using gp sum formula
# S = a / (1 - r)
# where r = prob_fail_s*prob_fail_z
#       a = prob_win_s

print(P_s / (1 - (1 - P_s) * (1 - P_z)))

    	  		  					 	 			   		