/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import  java.util.List;
import java.util.Comparator;
import java.util.Scanner;
import java.util.stream.Collectors;

/**
 *
 * @author macair
 *
 */
public class Palindrome {

    public static List<Integer> mirrorArrayListEven(List<Integer> array) {
        for (int i = array.size() - 1; i >= 0; i--) {
            array.add(array.get(i));
        }

        return array;

    }

    public static List<Integer> mirrorArrayListUneven(List<Integer> array) {
        for (int i = array.size() - 2; i >= 0; i--) {
            array.add(array.get(i));
        }

        return array;

    }

    public static List<Integer> generatePalindrome(ArrayList<Integer> array) {
        List<Integer> list=new ArrayList<>();
        int[] distinct =new int[array.stream().distinct().sorted(Comparator.reverseOrder()).collect(Collectors.toList()).size()];
        distinct[0]=1;

        list=array.stream().distinct().sorted(Comparator.reverseOrder()).collect(Collectors.toList());
        List<Integer>finalList=new ArrayList<>();
        List<Integer> arraySorted=array.stream().sorted(Comparator.reverseOrder()).collect(Collectors.toList());
        int position=-1;
        boolean isPalindrome=true;
        boolean hasMoreThanOneOdd=false;




        int j=0;


        for(int i=1;i<array.size();i++){
            if(arraySorted.get(i)!=arraySorted.get(i-1)){
                j++;
                distinct[j]++;

            }else if(arraySorted.get(i)==arraySorted.get(i-1)){
                distinct[j]++;
            }

        }
        for(int i=0;i<distinct.length;i++){
            if(distinct[i]%2!=0){
                position=i;

            }
        }
        for(int i=0;i<distinct.length;i++){
            if(distinct[i]<2){
               if(hasMoreThanOneOdd){
                   isPalindrome=false;
               }

                hasMoreThanOneOdd=true;


            }

        }




        for(int i=0;i<distinct.length;i++){
            distinct[i]/=2 + distinct[i]%2;
        }

        for(int i=0;i<distinct.length;i++){
            for(int h=0;h<distinct[i];h++){
                finalList.add(list.get(i));
            }

        }

        if(position>-1){
            finalList.add(list.get(position));
        }


        if (position==-1 && isPalindrome==true) {
            return  mirrorArrayListEven(finalList);

        }
        else if(isPalindrome==false){

            finalList.clear();
            finalList.add(0);
            return finalList;
        }
        else  {
            return  mirrorArrayListUneven(finalList);
        }

    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        List<Integer> finalList=new ArrayList<>() ;
        ArrayList<Integer> array = new ArrayList<>();

        int n = sc.nextInt();

        for (int i = 0; i < n; i++) {
            array.add(sc.nextInt());
        }

        finalList = generatePalindrome(array);
        Collections.reverse(array);
        if (finalList.get(0)==0) {
            System.out.println(0);
        } else {
            for (int i = 0; i < finalList.size(); i++) {
                System.out.print(finalList.get(i));
            }
        }

    }

}