import java.util.*;
public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner reader=new Scanner(System.in);
		String s=reader.next();
		int total=0;
		if(s.charAt(0)=='1') total++;
		if(s.charAt(1)=='1') total++;
		if(s.charAt(2)=='1') total++;
		System.out.println(total);
	}

}

/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