import random

N = int(input())
K = int(input())

trials = 500_000
win = 0
for _ in range(trials):
    a = 0
    for i in range(N):
        a += random.randint(1, 6)

    b = 0
    for i in range(N):
        if i < K:
            b += random.randint(4, 6)
        else:
            b += random.randint(1, 6)

    if a < b:
        win += 1

ans = win / trials
print(ans)