import java.util.Scanner;

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

		String n = sc.next();

		char[] str = new char[n.length()];

		int count = 0;
		for (int i = 0; i < n.length(); i++) {
			String tmp = String.valueOf(n.charAt(i));

			if (tmp.equals("1")) {
				count++;
			}
		}

		// 出力
		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