N = int(input())
ans = 0
cou = 0

for i in range(N, 6 * N + 1):
    cou += 1
    if cou <= 6 * (N - 1):
        n = i - 1
    else:
        n = 6 * N - i + 1
    s = i * n / (6 ** N)
    ans += s
print(round(ans, 2))