#include<bits/stdc++.h>
using namespace std;
int ans[100000001];
int main(){
	int n;
	while(cin>>n&&n!=0)
	{
		int s=0;
		while(n>=3)
		{
			s+=n/3;
			n=n/3+n%3;
		}
		if(n==2)
		{
			s++;
		}
		cout<<s<<endl;
	}
	return 0;
}