题解 | #汽水瓶#

import sys

def buy(number):
    sum = 0
    while True:
        if number == 2:
            sum += 1
            break
        elif number == 1:
            break
        news = number // 3
        number = number - (news) * 3  + news
        sum += news
    return sum



groups = []
for line in sys.stdin:
    groups.append(int(line))
for i in groups[:-1]:
    print(buy(i))