import java.util.Scanner;


public class digitsum {
	
	public static void main(String[] args){
		
		Scanner kboard =  new Scanner(System.in);
		char[] num = kboard.next().toCharArray();
		
		int result = 0;
		for (char c: num){
			result += Integer.parseInt(c +"");
		}
		System.out.println(result);
		kboard.close();
	}
	
}