# [2012北大校赛]Do Not Gamble

时间限制：10s 空间限制：128MB

### 题目描述

Have you ever gambled? I wish you not. Being a professional gambler for three years, I learned every

trick they play. Gambling is has nothing to do with luck. It is all about cheating.One of the most

elementary tricks is "mercury dice". Instead of being solid, there is a hollow chamber, filled with

mercury, inside of the dice. This little modification makes the dice asymmetric, so that, the probab

ility of each outcome is not equal. Imprecisely, which face is up, depends on the previous state.To

simplify the model, we use "mercury coin" here. As we mentioned, the state (head or tail) after toss

ing depends on the state before. The probability of that the two states are same, is p. For example,

if the head side is up now, the probability that, the coin is still head up after tossing is p. And

the probability that the tail side come up is 1-p. If p=0.5, it is a common coin. When p≠ 0.5, thi

s coin is mercury coin. Assume the coin is head up now. After we toss Ntimes, what is the probabilit

y that, the number of heads is less than a certain number K?

### 输入格式

The test file contains multiple lines, and each line is a test case.

Each test cases consists of three numbers

N K p

N and K are integers, and p is a float number.

N ≤ 30000

K ≤ N

0 ≤ p ≤ 1

### 输出格式

For each test case, output the probability that, after tossing N times, the number of heads is less

than K. Rounded to the three digit after the decimal point.

### 样例输入

171 88 0.107

### 样例输出

0.83785

### 提示

没有写明提示

### 题目来源

没有写明来源