import java.util.*;

public class Main{
	public static void main(String[] args){
    	Scanner sc = new Scanner(System.in);
      	String line = sc.nextLine();
      	String[] num = line.split("");
      	
      	int count = 0;
      	if(num[0].equals("1")){
        	count++;
        }
      	if(num[1].equals("1")){
        	count++;
        }
      	if(num[2].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