n = int(input())
K = int(input())

taro = {0:1}
for _ in range(n - K):
    tmp = {}
    for k, v in taro.items():
        for i in range(1, 7):
            tmp[k + i] = tmp.get(k + i, 0) + v
    taro = tmp
    
for _ in range(K):
    tmp = {}
    for k, v in taro.items():
        for i in range(4, 7):
            tmp[k + i] = tmp.get(k + i, 0) + v * 2
    taro = tmp

jiro = {0:1}
for _ in range(n):
    tmp = {}
    for k, v in jiro.items():
        for i in range(1, 7):
            tmp[k + i] = tmp.get(k + i, 0) + v
    jiro = tmp
    
div = 0
cnt = 0
for k1, v1 in taro.items():
    for k2, v2 in jiro.items():
        div += v1 * v2
        if k1 > k2:
            cnt += v1 * v2
print(cnt / div)