Mock1_1

import java.util.Scanner;


public class Main {



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

        String number = scanner.nextLine();
        int n=0;

        for(int i = 0; i < number.length(); i++){
            char ch = number.charAt(i);
            if(Character.isDigit(ch)){
                n += ch - '0';

            }
        }
        while(n>9){
            int newN = 0;

            while(n>0){
                newN += n % 10;
                n /= 10;
            }

            n = newN;


        }
        System.out.println(n);
    }


}