import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        for (int i = 1; i < 100; i++) {
            n = calc(n);
        }
        System.out.println(n);
    }
    
    static int calc(int x) {
        int ans = 0;
        while (x > 0) {
            ans += x % 10;
            x /= 10;
        }
        return ans;
    }
}