import java.util.*;

public class Lab2 {
	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		int n = s.nextInt();

		int sum = 0;
		for (int i = 0; i < 4; i++) {
			sum = sum + n % 10;
			n = n / 10;
		}

		System.out.println(sum);
	}
}