题解 | #汽水瓶# 递归

import sys

num_list = []


def drink(num, final_num = 0):

    buy = num//3
    res = num%3
    total = buy + res
    final_num += buy

    if total > 1:
        if total == 2:
            total += 1
        return drink(total, final_num)
    else:
        return final_num

while True:
    num = int(input())
    if num == 0:
        break
    final = drink(num)
    num_list.append(final)

print(*num_list, sep='\n')