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 a/b for SmallR while c/d 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 a,b,c,d (1<=a,b,c,d<=1000, 0<a/b<1, 0<c/d<1).
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 1e-6.
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