#include <iostream>
#include <math.h>

using namespace std;
int unos, temp1, b, temp2,rjes;
int main()
{
    cin>>unos;
    temp1=unos/10;
    while(temp1>=1)
    {
        temp1=temp1/10;
        b++;
    }
    while(b>=0)
    {
        temp2=unos/pow(10,b);
        rjes+=temp2%10;
        b=b-3;
    }
    cout<<rjes;
}