题解 | #汽水瓶#

alls = []
while True:
    try:
        alls.append(int(input().strip()))
    except EOFError:
        break
        
        
for n in alls:
    num = 0 
    if n > 0:
        if n == 1:
            print(0)
        elif n == 2:
            print(1)
        else:
            while True:
                x = int(n / 3) # 商：表示可以兑换的瓶子数目
                y = int(n % 3)  # 余数，表示兑换后剩余的瓶子数目
                num += x
                n = x + y
                if int(n) > 3:
                    continue
                if int(n) == 3:
                    num += 1
                    break
                elif int(n) == 2:
                    num += 1
                    break
                else:
                    break
        print(int(num))