import itertools as it
def denomi(dices):
    res = 1
    for i in set(dices):
        res *= fact[dices.count(i)]
    return res
fact = [1]+[reduce(lambda a,b:a*b,range(1,i+1)) for i in range(1,11)]

N = int(raw_input())
K = int(raw_input())
d1 = [0]*61
d2 = [0]*61
for dices in it.combinations_with_replacement(range(1,7),N):
    d1[sum(dices)] += fact[N]/denomi(dices)
for dices1 in it.combinations_with_replacement(range(1,7),N-K):
    for dices2 in it.combinations_with_replacement([4,5,6],K):
        d2[sum(dices1)+sum(dices2)] += fact[N-K]/denomi(dices1) + fact[K]/denomi(dices2)

sum1 = sum(d1)
sum2 = sum(d2)
ans = 0.0
for i in range(61):
    ans += 1.0*d2[i]/sum2*sum(d1[:i])/sum1
print ans