import random
N = int(input())
K = int(input())
result = [0, 0, 0]
NUM = (10 ** 5) * 2
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:
        result[0] += 1
    if taro < jiro:
        result[1] += 1
    if taro == jiro:
        result[2] += 1
print(result[0]/NUM)