import java.util.Scanner;
public class Main{
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		String a = sc.next();
		char[] ac = a.toCharArray();
		int count = 0;
		if (ac[0] == '1') count++;
		if (ac[1] == '1') count++;
		if (ac[2] == '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