import random
N = int(input())
K = int(input())

total = 0
win = 0
for i in range(10**6):
  a = 0 # 次郎君のサイコロ
  b = 0 # 太郎君のサイコロ
  for j in range(N):
    a += random.randint(1, 6)
    if j < K:
      b += random.randint(4, 6)
    else:
      b += random.randint(1, 6)

  if b > a:
    win += 1
  total += 1

print(win/total)