def E(x):
	global K
	if dp[x] != -1:
		return dp[x]
	if x >= K:
		return 1.0
	else:
		ret = 0.0
		for i in range(1,6 + 1):
			ret += E(x + i) / 6
		ret += 1
		dp[x] = ret
		return dp[x]
K = int(input())
dp = [-1 for i in range(K * 7 + 1)]
print (E(0) - 1)