Archer

2000ms

262144K

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 $\text{[math]}$ for SmallR while $\text{[math]}$ for Zanoes. The one who shoots in the target first should be the winner.

Output the probability that SmallR will win the match.

Input:

A single line contains four integers $\text{[math]}$ .

Output:

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.

Sample Input:

1 2 1 2

Sample Output:

0.666666666667

Informação

Provedor Codeforces

Código CF312B