#include <stdio.h>

int main()
{
    int n;
    while(scanf("%d",&n))
    {
        int k=0;
        if(n == 1 || n == 0)
            break;
        while(n>=3)
        {
            k += n /3;
            n = n /3 + n % 3;
        }
        if(n == 2)
        {
            k++;
        }
        printf("%d\n",k);
    }
    return 0;
}