class Calc0058
  EPS = 1e-3

  def initialize(args)
    args = args.map { |l| l.chomp.split(/\s+/) }
    @n = args.shift.first.to_i
    @k = args.shift.first.to_i
  end

  def run
    sais_taro = Array.new(@n - @k) { (1..6).to_a } + Array.new(@k) { [4, 5, 6] * 2 }
    sais_jiro = Array.new(@n) { (1..6).to_a }

    hist_taro = make_hist(sais_taro, [1])
    hist_jiro = make_hist(sais_jiro, [1])

    hist_jiro.map.with_index { |h, i|
      h * (hist_taro.drop(i + 1).inject(:+) || 0)
    }.inject(:+).to_f / 6 ** (@n * 2)
  end

  def make_hist(sais, hist)
    sais.each do |sai|
      hist = sai.map { |d| [0] * d + hist + [0] * (sai.max - d) }.transpose.map { |r| r.inject(:+) }
    end
    hist
  end
end

puts Calc0058.new(STDIN.readlines).run if __FILE__ == $0