说明

       There is a election between 2 persons. The election has p+q rounds. In each round, either person A or person B gets one vote. The probility that A gets a vote is equal to the probility that B gets a vote . Finally, person A gets p votes and person B gets q votes(p > q). Can you figure out the probability that in any round person A gets more votes than person B.

输入格式

       Multiple cases. Every case takes a line with the positive integers p and q(p > q, p and q are 32-bit-signed integers).

输出格式

      One case a line.Print the probability, with exactly 6 digits after the decimal point.

2 1

0.333333

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