import numpy as np
from scipy.linalg import null_space

K = int(input())
M = np.zeros((K, K + 1), dtype=int)
M[:, -1] = 6
for i in range(K):
    M[i, i + 1:min(i + 7, K)] = 1
    M[i, i] = -6
    M[i, 0] += max(i + 6 - K, 0)

Ker = null_space(M).flatten()
print(Ker[0] / Ker[-1])