#include<iostream>
using namespace std;
int main ()
{
    int n;
    while (cin >> n)
    {
        int ans = 0;
        if (n == 0)break;
        while (n >= 3)
        {
            ans += n / 3;
            n = n / 3 + n % 3;
        }
        if (n == 2)ans++;
        cout << ans << endl;
    }
}