Description:
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 $${ \frac { a } { b } }$$ for SmallR while $$\frac{c}{d}$$ for Zanoes. The one who shoots in the target first should be the winner.
Output the probability that SmallR will win the match.
Input Format:
A single line contains four integers $$a,b,c,d \ (1 \leq a,b,c,d \leq 1000, 0 < \frac{a}{b} < 1, 0 < \frac{c}{d} < 1)$$.
Output Format:
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.
Note:
None