N, K = 2.times.map{ gets.to_i }
T = 1_000_000
n = T.times.count do
  t = K.times.inject(0){|s,i| s + rand(6) + 1 } + (N - K).times.inject(0){|s,i| s + rand(3) + 4 }
  j = N.times.inject(0){|s,i| s + rand(6) + 1 }
  t > j
end
puts n.to_f / T