#Digital Roots#写个while循环就行

//Java写法
import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (sc.hasNextInt()) {
            int n = sc.nextInt();
            while (n > 9) {
                int sum = 0;
                int temp = n;
                while (temp > 0) {
                    sum += temp % 10;
                    temp /= 10;
                }
                n = sum;
            }
            System.out.println(n);
        }
    }
}
#Python写法
while True:
    try:
        n = int(input())
        while n > 9:
            n = sum(map(int, str(n)))
        print(n)
    except:
        break