C :

#include <stdio.h>

int main()
{
    //freopen("a.in", "r", stdin);
    //freopen("A.out", "w", stdout);
    int n;
    while(scanf("%d", &n), n)
    {
        printf("%d\n", n / 2);
    }
    return 0;
}

C++ :

#include<iostream>
using namespace std;
int main()
{
	int n;
	int sum,count;            //能兑换到的瓶数 
	while(cin>>n&&n!=0)
	{
		sum=0;count=0;
		if(n>=3)
		{
			while(n>2)
			{
				sum=n/3;
				n=n-3*sum+sum;        //剩余的瓶数
				count+=sum;
			}
			if(n==2)
			{
				count++;
			}
		cout<<count<<endl;
		}
		else
		{
			cout<<0<<endl;
		} 
	}	
}