import java.util.*;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		String s = sc.next();

		int count = 0;
		for(String value : s.split("")) {
			if(value.equals("1")) count++;
		}

		System.out.println(count);

	}

	public static void print(Object o) {
		System.out.print(o);
	}

	public static void println(Object o) {
		System.out.println(o);
	}
}
/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