Problem: 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 <image> for SmallR while <image> 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 <image>.

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.

Examples

Input

1 2 1 2


Output

0.666666666667

Solution (in PYTHON3):

Solution:
def prob():
    ''' Using Geometric series sum '''
    n = input().split()
    arc = float(n[0]) / float(n[1])
    zan = float(n[2]) / float(n[3])

    return arc * (1/(1-((1-arc)*(1-zan))))

# Running the Program
print(prob())