#!/usr/bin/env ruby

def binom n, k
  prod = 1
  (1..k).each { |j|
    prod *= (n+1-j)/j
  }

  return prod
end

def bdist k, p, n
  binom(n, k)*(p**k)*(1-p)**(n-k)
end

puts bdist(ARGV[0].to_f, ARGV[1].to_f, ARGV[2].to_f)