题解 | #汽水瓶#

# 递归
def change(num):
    ch = num // 3  # 可换的瓶子
    a = num // 3 + num % 3  # 换完后的空瓶
    if a < 2:
        ch += 0
    elif a == 2:
        ch += 1
    else:
        ch += change(a)
    return int(ch)


while True:
        n = int(input())
        if n == 0:
            break
        print(change(n))