题解 | #汽水瓶#

#!/usr/sbin/python
# -*- coding: utf-8 -*-

def c2one(num):
    if num > 2:
        return int(num / 3), num % 3
    elif num == 2:
        return 1, 0
    else:
        return 0, 0


while True:
    try:
        input_i = int(input())
        result_count = input_i
        result = 0
        if input_i == 0:
            break
        while result_count > 1:
            result_i = c2one(result_count)
            result_count = int(result_i[0]) + int(result_i[1])
            result += int(result_i[0])
        print(result)
    except:
        break