import random

def win(n, k):
    n -= k
    sum = 0
    for i in range(k):
        sum += random.randint(4, 6)-random.randint(1, 6)
    for i in range(n):
        sum += random.randint(1, 6)-random.randint(1, 6)
    return sum>0

n = int(input())
k = int(input())

trying = 100000
cnt = 0
for i in range(trying):
    if(win(n, k)): cnt += 1
print(cnt/trying)