import java.util.Scanner;

public class HelloWorld {

	    public static void main(String[] args) throws Exception {

	    	Scanner sc = new Scanner(System.in);
	    	int a0 = sc.nextInt();
	    	for (int i = 0; i < 100; i++) {
	    		a0 = nextA(a0);
	    	}

	    	System.out.println(nextA(a0));

	    	}

	    static int nextA(int a) {
	    	int next_a = 0;
	    	while (a > 0) {
	    		next_a += a % 10;
	    		a /= 10;
	    	}

	    	return next_a;
	    }

}