import random

#N = 10
#K = 0

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

def dice1_6():
	return random.randint(1,6)

def dice4_6():
	return random.randint(4,6)

def main():
	trials = 100000
	taro_win = 0
	for i in range(trials):
		Taro = 0
#		Jiro = 0
#		for j in range(N):
#			Jiro += dice1_6()
		for j in range(N-K):
			Taro += dice1_6()
		for j in range(K):
			Taro += dice4_6()
		if Taro>3.5*N:
			taro_win += 1
	print(taro_win/trials)

if __name__ == '__main__':
	main()