HashSet

import java.util.*;
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String s = sc.nextLine();
        Set<Character> set = new HashSet<>();
        for(int i = s.length() - 1; i >= 0; i--) {
            if(set.add(s.charAt(i))) {
                System.out.print(s.charAt(i));
            }
        }
    }
}