Score : 100 points
In an electric circuit, when two resistors R_1 and R_2 are connected in parallel, the equivalent resistance R_3 can be derived from the following formula:
Given R_1 and R_2, find R_3.
The input is given from Standard Input in the following format:
R_1 R_2
Print the value of R_3.
The output is considered correct if the absolute or relative error is at most 10^{-6}.
2 3
1.2000000000
100 99
49.7487437186