import java.util.Comparator;
import java.util.Scanner;
import java.util.TreeSet;

public class Test5 {

	public static void main(String[] args) {
		Scanner sc=new Scanner(System.in);
		System.out.println("請輸入一個字串：");
		String line=sc.nextLine();
		char[] arr=line.toCharArray();
		
		TreeSet<Character> ts=new TreeSet<>(new Comparator<Character>() {

			@Override
			public int compare(Character s1, Character s2) {
				int num=s1.compareTo(s2);
				return num==0?1:num;
			}
		});
		for (char c : arr) {
			ts.add(c);//自動裝箱
		}
		for(Character c:ts) {
			System.out.print(c);
		}
	}

}