#include<bits/stdc++.h>
using namespace std;
int n,sum,num;
int main()
{
	while(cin>>n)
	{
		sum=0;
		if(n==0) break;
		while(n>=3)
		{
			num=n/3;
			sum+=num;
		    n%=3;
		    n+=num;
		}
		if(n==2) sum++;
		cout<<sum<<endl;
	}
	return 0;
}