import java.util.Scanner;

public class Main
{
    public static void main(String[] args) 
    {
        Scanner scan = new Scanner(System.in);
        String s = scan.next();
        String one = "1";
        int output=0;

        String[] sr = s.split("");

        if(sr[0].equals(one))
        {
            output++;
        }
        if(sr[1].equals(one))
        {
            output++;
        }
        if(sr[2].equals(one))
        {
            output++;
        }
        System.out.println(output);
    }
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz