import random

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

ANS=0
tests=10**6
for i in range(tests):
    A=0
    B=0
    for j in range(N):
        if j<K:
            A+=random.randint(4,6)
            B+=random.randint(1,6)
        else:
            A+=random.randint(1,6)
            B+=random.randint(1,6)
    if A>B:
        ANS+=1
    
print(ANS/tests)