#include <iostream>
using namespace std ;
int main()
{
    int n,rest=0,raspuns=0;
    cin >> n ;
    raspuns = n % 3 ;
    while (n != 0)
    {

        if (n % 10 % 3 == raspuns)
        {
            rest ++ ;
        }

        n=n/10 ;

    }

    cout << rest ;
    return 0 ;

}