import java.util.Scanner;

public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		sc.close();

		for (int i = 1; i < 100; i++) {
			int x = 0;
			while (n > 0) {
				x += n % 10;
				n /= 10;
			}
			n = x;
		}
		System.out.println(n);
	}
}