Mock1_1

import java.text.DecimalFormat;
import java.util.Scanner;


public class Main {



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

        DecimalFormat df = new DecimalFormat("0.###");
        String numbers = scanner.nextLine();  //String would be 55
        Double y = Double.parseDouble(numbers);
        double number = 0;
        String number2 = "";
        if(y < 0){
             number = Math.abs(y);
             number2 = df.format(number);

        }



        double sum = 0;

        for (char c : number2.toCharArray()) {
            sum += c - '0' ;
        }
        String sum2 = df.format(sum);
        //String sum3 = sum2;
        double sum4 = Double.parseDouble(sum2);

        String numbers2 = sum2;
        if (Double.parseDouble(sum2) > 9) {
            sum4=0;
            for (char b : numbers2.toCharArray()) {
                sum4 += b - '0' ;
            }

        }
        System.out.printf("%.0f",sum4);
    }


}