def exp(N):
    A = [0] * (N + 1)
    B = [0] * (N + 1)

    inv = 1.0 / 6

    for i in range(N - 1, -1, -1):
        for j in range(1, 7):
            if i + j > N:
                A[i] += inv
                B[i] += inv
            else:
                A[i] += (A[i + j] + 1) * inv
                B[i] += B[i + j] * inv
    return A[0] / (1 - B[0])


N = int(raw_input())

print exp(N)