#include<iostream>
using namespace std;
 
int main()
{
	int  num,res ;
	while (cin >> num && num != 0)
	{
		res = 0;
	 	while (num >= 3)
		{
			res += num / 3;
			num = num % 3  + (num / 3) ;	
		}
		if (num == 2) res+=1;
		cout << res <<endl;
	}
    return 0;
}