题解 | #汽水瓶#

#为啥int(line.split()[0]) ==0 改成line[:-1]=='0'就不对了，输入0时会输出一个0
import sys

for line in sys.stdin:
    if int(line.split()[0]) ==0:
        break
    a = int(line.split()[0])
    sum = 0
    while a // 3 >= 1 or a == 2:
        sum = sum + a // 3
        a = a // 3 + a % 3
        if a == 2:
            a = a + 1
        else:
            continue
    print(sum)