import java.util.Scanner;

public class Main {

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

        String input = scanner.nextLine().replace(".","").replace("-","");
        double number = Double.parseDouble(input);
        while(number > 9 || number < 0) {
            number = sumDigits(number);
        }
        System.out.println((int)(number));
    }

    private static double sumDigits(double input) {
      int sum = 0;

        while (input > 0) {
            sum += input % 10;
            input /= 10;
        }
        return sum;
    }
}