n = int(input())

dp = [ 0.0 ] * (n + 6)
dp[0] = 1.0

answer = 0
iters = 0
while sum(dp) > 1.0e-20:
	ndp = [ 0.0 ] * (n + 6)
	for i in range(n):
		for j in range(1, 7):
			ndp[i + j] += dp[i] / 6
	for i in range(n + 1, n + 6):
		ndp[0] += ndp[i]
		ndp[i] = 0
	dp = ndp.copy()
	iters += 1
	answer += ndp[n] * iters

print(answer)