import java.util.Scanner;

public class Main{
	public static void main(String[]args){
		Scanner sc=new Scanner(System.in);
		String a=sc.next();
		String s[]=new String[3];
		int count=0;
		s=a.split("");
		for(int i=0;i<3;i++){
			if(s[i].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