1231 - Coin
Time Limit : 1 Second
Memory Limit : 128 MB
Submission: 43
Solved: 12
- Description
- Suppose Liang Liang has N identical coins. Note that the coin is not fair, which means that when tossed, the probability of head facing up is not equal to that with tail facing up. Meanwhile, Liang Liang doesn't have any information about what probability is more probable. In order to get clearer about the characteristic of these coins, Liang Liang decides to carry out an experiment with them like this:
He tosses them at the same time, and found that K of them have head facing up and others with tail facing up.
Now Liang Liang decides to do that again, but before that, he wants to predict the outcome of it. However, he found it a little confusing, so he turned to you for help.
As a sophisticated programmer, you decide to calculate the expectation of the number of coins with head facing up in the next experiment then tell Liang Liang the result. Now it's your turn.
- Input
- Input have multiple test cases and terminates with EOF.
Each case has a line containing two integers N(0<N<=100), K(0<=K<=N).
- Output
- For each case output one number indicating the expectation in one line rounded to the thousands.
- sample input
-
10 5 100 0
- sample output
-
5.000 0.980
- hint
- When some coins are tossed at the same time, any one doesn't affect the outcome of other coins.
- source
- Isun