#include <iostream>
#include <fstream>
#include <cmath>

using namespace std;


int main()
{
    long long int n,s=0,x,nrcif=0,nr=0;
    int p=1;
    cin>>n;
    x=n;
    while (x)
    {
        s+=x%10;
        nrcif++;
        x/=10;
    }
    while(nrcif!=0)
    {
        int aux=(n/p)%10;
        while (aux>9)
            aux/=10;
        if ((s-aux)%3==0)
        {
            nr++;
        }
        p*=10;
        nrcif--;
    }
    cout<<nr;

    return 0;
}