import java.util.*;
public class Main {
	public static void main(String[] args){
      Scanner sc = new Scanner(System.in);

      String s = sc.next();
      char[] ch = s.toCharArray();
      
      int cnt = 0;
      if(ch[0] == '1') {
        cnt++;
      }
      if(ch[1] == '1') {
        cnt++;
      }
      if(ch[2] == '1') {
        cnt++;
      }
      
      System.out.println(cnt);
      
      


	}
}
/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