题解 | #汽水瓶#

lis = []
while True:
    num = input()
    if num == "0":
        break
    else:
        lis.append(num)
lis1 = []
for n in lis:
    tatol = 0
    n = int(n)
    while n >= 3:
        a_int = n // 3
        tatol += a_int
        a_left = n - 3 * a_int
        n = a_int + a_left
        if n == 2:
            tatol += 1
    else:
        lis1.append(tatol)
for ans in lis1:
    print(ans)