import java.util.*;

public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        String x = sc.nextLine();
        int n = 0;
        int temp = 0;
        while((n = x.length())!=1){
            temp = 0;
            for(int i = 0; i < n; i++){
                temp += Integer.valueOf(x.charAt(i)-'0');
            }
            x = String.valueOf(temp);
        }
        System.out.println(temp);
    }
}