def func(num):
    q, r = divmod(num, 3)
    k = q + r  # 剩余的空瓶子
    if k == 2:
        q += 1
    elif k > 2:
        q += func(k)
    return q

while True:
    n = int(input())
    if n == 0:
        break
    else:
        print(func(n))

递归思想