题解 | #汽水瓶#

import sys


def recursive(emptys: int, count: int) -> int:
    if emptys < 2:
        return count
    elif emptys == 2:
		# 两个空瓶可以借一个
        return count + 1

    bottles = emptys // 3
    remains = emptys % 3
    count += bottles
    emptys = bottles + remains

    return recursive(emptys, count)


for line in sys.stdin:
    if line.strip() == "0":
        break
    emptys = line.strip()
    print(recursive(int(emptys), 0))