import java.util.Scanner;

public class Main {

	private static Scanner sc;

	public static void main(String[] args) {

		sc = new Scanner(System.in);
		String str = sc.next();
		int count = 0;

		if (str.substring(0,1).contentEquals("1")) count+=1;
		if (str.substring(1,2).contentEquals("1")) count+=1;
		if (str.substring(2,3).contentEquals("1")) count+=1;

		System.out.print(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