package stringAndTextProcessing;

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
import java.util.TreeSet;

public class palindromes {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String text = scanner.nextLine();

        String textReversed = "";
        for (int i = text.length() - 1; i >= 0; i--) {
            textReversed += text.charAt(i);
        }

        String[] firstCompare = text.split("[^A-za-z0-9]+");
        String[] secondCompare = textReversed.split("[^A-za-z0-9]+");

        TreeSet<String> result = new TreeSet<>();
        for (int i = 0; i < firstCompare.length; i++) {
            for (int j = 0; j < secondCompare.length; j++) {
                if (firstCompare[i].equals((secondCompare[j]))) {
                    result.add(secondCompare[j]);
                }
            }
        }

        System.out.println(result);

    }
}