题解 | 汽水瓶

import sys

for line in sys.stdin:
    a = line.split()
    # print(int(a[0]) + int(a[1]))
    null = int(a[0])
    total = 0
    if null == 0:
        break
    while null > 1:
        num = null // 3
        null = num + null % 3
        if null == 2: # 只有还剩两个空瓶的时候才能借一个，刚好满3个换一瓶汽水，喝完还给老板一个空瓶
            null += 1
        total += num
    print(total)