package com.scalefocus;

import java.util.*;
import java.util.stream.Collectors;

public class Main {

    public static void main(String[] args) {
	    Scanner sc = new Scanner(System.in);

	    String[] words = sc.nextLine().split(" ");

        LinkedHashMap<String, Integer> counts = new LinkedHashMap<>();
        for (String word : words) {
            String lowerWord = word.toLowerCase();
            if (!counts.containsKey(lowerWord)) {
                counts.put(lowerWord, 1);
            } else {
                counts.put(lowerWord, counts.get(lowerWord) + 1);
            }
        }


//        List<Integer> result = new ArrayList<>(); - if used with other type than String
        String result = counts.entrySet().stream()
                .filter(x -> x.getValue() % 2 != 0)
                .map(x->x.getKey()) // .getValue() for word counts
               // .collect(Collectors.toList()); - for other type of mappable (used in map) value
                .collect(Collectors.joining(", ")); //for strings only
        System.out.println(result);
        /*ArrayList<String> result = new ArrayList<>();
        for (Map.Entry<String, Integer> entry : counts.entrySet()) {
            if(entry.getValue() % 2 != 0) {
                result.add(entry.getKey());
            }
        }*/

        //System.out.println(String.join(", ", result));
    }
}