N,K=$<.map &:to_i

def f(n, k)
  dp = {}
  g = ->sum, i{
    dp[[sum,i]] ||= if i < 0 && sum == 0
      1
    elsif i < 0 || sum < 1
      0
    elsif i < k
      (4..6).map{|j| g[sum - j, i - 1] }.sum
    else
      (1..6).map{|j| g[sum - j, i - 1] }.sum
    end
  }
  sums = (n..n*6).map{|sum| g[sum, n-1] }
  sum_of_sums = sums.sum
  sums.map{|sum| sum.quo(sum_of_sums) }
end

taro = f(N, K)
jiro = f(N, 0)
ans = (1...taro.size).map{|i|
  (0...i).map{|j|
    taro[i] * jiro[j]
  }.sum
}.sum
puts "%.3f" % ans