题解 | 汽水瓶

def ex(n):
    if n == 2:
        return 1 
    if n == 1:
        return 0
    if n == 0:
        return 0
    y = n//3
    a = n-3*y
    b = y+a
    return y + ex(b)
    
while True:
    n = eval(input())
    if n == 0:
        break
    if n > 2:
        n=ex(n)
    print(n)