import java.util.Scanner;

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


        double number = Double.parseDouble(user_input.nextLine());
        int sum = 0;

        if (number < 0) {
            number = Math.abs(number);
        }

        String number1 = number + "";

        for (char c : number1.toCharArray()) {
            if (c != '.') {
                sum += Integer.parseInt(String.valueOf(c));
            }
        }

        number = sum;
        int n = (int) number;


        while (n != 0) {
            if (sum > 9) {
                sum = 0;
                sum = sum + n % 10;
                n = n / 10;
                sum = n + sum;

            } else {
                System.out.println(sum);
                break;
            }
        }


    }
}