#include <iostream>
#include <cmath>
using namespace std;
long long n,r,s;
int nc(int x)
{
    int nrcif=0;
    while(x)
        nrcif++,x/=10;
    return nrcif;
}
int sc(int x)
{
    int sc;
    while(x)
        sc+=x%10,x/=10;
    return sc;
}
int main()
{
    cin>>n;
    s=sc(n);
    while(n)
    {
        if(n%10%3==s%3)
            r++;
        n/=10;
    }
    cout<<r;
    return 0;
}