
ZOJ Problem Set  3374
Recently, a total of 786 girls in Gensokyo sat in a circle, 203 of them were selected as the characters of next Touhou ACT game by draw. Unfortunately, Letty Whiterock didn't win, and she thought it was strange that the nine girls (Reimu, Yukari, Marisa, Alice, Sakuya, Remilia, Youmu, Yuyuko and Sanae) sitting adjacently all won. The expert (proclaimed by herself) Assume that m girls out of n are selected in eqaul probability, it will be helpful if you can calculate the right probability that there are nine adjacent girls. Remember that the n girls sit in a circle, so the first one is adjacent to the last one. InputThere are multiple cases. Each cases consists of two integers: 1 ≤ n ≤ 1000 and 1 ≤ m ≤ n. OutputFor each case, output the probability. Answer having an absolute error less than 1e5 will be accepted. See sample for more details. Sample Input10 9 17 15 18 16 786 203 Sample Output100.000000% 87.500000% 94.117647% 0.263488% ReferencesAuthor: WU, Zejun Source: ACM × Touhou Contest: ZOJ Monthly, August 2010 