class Integer
  def factorial
    (1..self).inject(1){|r, i| r * i}
  end
  def combination(n)
    self.factorial / (n.factorial * (self - n).factorial)
  end
end
def pepsi(m, n)
  result = (0..m).inject(0){|r, i| r + (-1)**i * m.combination(i) * (m - i)**n}
  (result * 10000000000000000 / m**n).to_f / 10000000000000000
end
puts pepsi(ARGV[0].to_i, ARGV[1].to_i)