import java.util.Scanner;
public class Main {
	public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        int c = 0;
        if (s.charAt(0) == '1') c++;
        if (s.charAt(1) == '1') c++;
        if (s.charAt(2) == '1') c++;
        System.out.println(c);
	}
}
/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