import random
N=int(input())
K=int(input())
w=0
c=755000
a=random.randrange
r=range
for i in r(c):
	t=0
	j=0
	for _ in r(N):
		j+=a(1,7)
	for _ in r(K):
		t+=a(4,7)
	for _ in r(N-K):
		t+=a(1,7)
	if t>j:
		w+=1
print(w/c)