import sys
import numpy as np
input=lambda:sys.stdin.readline().rstrip()
K=int(input())
A=[[int(i==j) for i in range(K)] for j in range(K)]
b=[[1] for i in range(K)]
for i in range(K):
	for j in range(1,7):
		if i+j<K:
			A[i][i+j]-=1/6
		elif i+j>K:
			A[i][0]-=1/6
A=np.array(A)
b=np.array(b)
print((np.linalg.inv(A)@b)[0][0])