import java.util.*;
public class Main {
	public static void main(String[] args){
	  Scanner sc = new Scanner(System.in);
      //文字列
      String s =sc.nextLine();
      int c = 0;
      if(s.charAt(0) == '1'){
      	c++;
      }
      if(s.charAt(1) == '1'){
      	c++;
      }
      if(s.charAt(2) == '1'){
        c++;
      }
      
      System.out.print(c);
		
	}
}

/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