import sys
read = sys.stdin.read
readline = sys.stdin.readline
readlines = sys.stdin.readlines

import random

n, K = map(int, read().split())
ITER = 10**6
cnt = 0
for _ in range(ITER):
    taro, jiro = 0, 0
    for i in range(n-K):
        taro += random.randint(1, 6)
    for i in range(K):
        taro += random.randint(4, 6)
    for i in range(n):
        jiro += random.randint(1, 6)
    if taro > jiro:
        cnt += 1
print(cnt / ITER)