495. Kids and Prizes

Time limit per test: 0.25 second(s)
Memory limit: 262144 kilobytes
input: standard
output: standard



ICPC (International Cardboard Producing Company) is in the business of producing cardboard boxes. Recently the company organized a contest for kids for the best design of a cardboard box and selected M winners. There are N prizes for the winners, each one carefully packed in a cardboard box (made by the ICPC, of course). The awarding process will be as follows: The management of the company would like to know how many prizes will be given by the above process. It is assumed that each winner picks a box at random and that all boxes are equally likely to be picked. Compute the mathematical expectation of the number of prizes given (the certificates are not counted as prizes, of course).

Input
The first and only line of the input file contains the values of N and M ().

Output
The first and only line of the output file should contain a single real number: the expected number of prizes given out. The answer is accepted as correct if either the absolute or the relative error is less than or equal to 10-9.

Example(s)
sample input
sample output
5 7
3.951424

sample input
sample output
4 3
2.3125




Online Contester Team © 2002 - 2010. All rights reserved.