#include <iostream>
using namespace std;
//
注意两瓶的时候可以借一瓶跟老板换
每次输入循环要重置chag数量
kcount是空瓶数,chag是可交换的瓶子数
//
int main()
{
    int kcount;
    int chag ;
    cin >> kcount;

    while(kcount >0)
    {
        chag = 0;
        while(kcount>=2)
        {   

            chag =chag+ kcount/3;
            kcount = kcount/3 + kcount%3;
            if(kcount==2)
            {
                chag ++;
                break;
            }
        }
    cout << chag <<endl;  
    cin>>kcount;
    }
    return 0;
}