import sys,time,random
input=lambda:sys.stdin.readline().rstrip()
N,K=[int(input()) for i in range(2)]
T=time.time()
trial,win=0,0
while time.time()-T<4.8:
	trial+=1
	taro,jiro=0,0
	for i in range(N):
		taro+=random.randrange(6)+1
	for i in range(N-K):
		jiro+=random.randrange(6)+1
	for i in range(K):
		jiro+=random.randrange(3)+4
	win+=(jiro>taro)
print(win/trial)