import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String str = sc.next();
		String ss[] = new String[3];
		sc.close();

		int count = 0;
		for(int i = 0; i < ss.length; i++) {
			ss[i] = str.substring(i , i + 1);
			if(ss[i].equals("1")) {
				count++;
			}else {
				continue;
			}
		}

		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