import java.util.*;

public class Main {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        double a = input.nextInt();
        double result = 0;
        double test = 0;
        double test1 =0;

        if (a < 0) {
            a = a * -1;
        }
        result = result + (a % 10);

        for (int j = 0; j < a; j++) {
            a = a / 10;
            result = result + Math.floor(a % 10);
            test = result;

            if (a < 10) {
                break;
            }
        }
        if (test > 9) {
            result = 0;
            result= result+ (test % 10);

            for (int i = 0; i <result; i++) {
                test = test/10;
                result = result + Math.floor(test % 10);
                if (test < 10) {
                    break;
                }
            }
            test1=result;
        }
        else {
            System.out.println(result);

        }
        test=test1;

    }
        }