import random
N = int(input())
K = int(input())
win = 0
NUM = 300000
table = ([1] * K) + ([0] * (N-K))


random.seed()
for i in range(NUM):
    taro = 0
    jiro = 0
    for j in range(N):
        jiro += random.randrange(1, 7)
        if random.sample(table, 1) == [1]:
            taro += random.randrange(4, 7)
        else:
            taro += random.randrange(1, 7)
    if taro > jiro:
        win += 1
print(win/NUM)