import numpy as np
K = int(input())
A = np.zeros((K+1, K+1), dtype = np.float64)
for i in range(K + 1):
    A[i, i] = 1.0
    p = 1.0
    for j in range(1, 7):
        if i + j > K:
            break
        A[i, i + j] -= 1.0 / 6.0
        p -= 1.0 / 6.0
    if i < K:
        A[i, 0] -= p

B = np.ones(K+1, np.float64)
B[K] = 0.0

E = np.linalg.solve(A, B)
print(E[0])