import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        try (Scanner sc = new Scanner(System.in)) {
            int N = sc.nextInt();
            int a = N;
            for (int i = 2; i < 100; i++) {
                int sum = 0;
                while (a != 0) {
                    sum += a % 10;
                    a /= 10;
                }
                a = sum;
            }
            System.out.println(a);
        }
    }
}