java解法（完全按题目思路）

import java.util.Scanner;


public class Main{

    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        while(sc.hasNext()){
            int n = sc.nextInt();

            if(n == 0) return;

            int sum = 0,yu = 0;
            while(n >= 3){
                yu = n % 3;
                //加上手里能够换取瓶子的数量
                sum += n / 3;
                //更新每次换取瓶子后所剩瓶子数
                n = n / 3 + yu;
            }
            if(n == 2){
                sum++;
            }
            System.out.println(sum);

        }
    }
}