import java.util.*;
 
public class Main {
    public static void main(String[] args) throws Exception {
        // Your code here!
        
        Scanner scan = new Scanner(System.in);
        
        String s = scan.nextLine();
        
        String s1 = s.substring(0 , 1);
        String s2 = s.substring(1 , 2);
        String s3 = s.substring(2 , 3);
        
        int count = 0;
        
        if (s1.equals("1")) {
            count++;
        } if (s2.equals("1")) {
            count++;
        } if (s3.equals("1")) {
            count++;
        }
        
        System.out.println(count);
    }
    
}
/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