import java.util.Map;
import java.util.Scanner;
import java.util.TreeMap;

public class Main {
    public static void main(String[] args) {
       Scanner in = new Scanner(System.in);
       int n = in.nextInt();
       String s = in.next();
       if (n == 1) {
           System.out.println(s);
           System.exit(0);
       }
       TreeMap<Character, Integer> map = new TreeMap<>();
       for (int i = 0; i < n; i++) {
            if (map.containsKey(s.charAt(i))) {
                map.put(s.charAt(i), map.get(s.charAt(i)) + 1);
            } else {
                map.put(s.charAt(i), 1);
            }
       }
       int oddCnt = 0;
       char oddChar = 0;
       for (Map.Entry<Character, Integer> entry : map.entrySet()) {
           if (entry.getValue() % 2 != 0) {
               oddCnt++;
               oddChar = entry.getKey();
           }
       }
       if (oddCnt > 1 || oddCnt == 1 && s.length() % 2 == 0) {
           System.out.println(-1);
           System.exit(0);
       }
       StringBuilder first = new StringBuilder();
       StringBuilder second = new StringBuilder();
       for (Map.Entry<Character, Integer> entry : map.entrySet()) {
           String l = String.valueOf(entry.getKey()).repeat((int) Math.floor(entry.getValue() / 2.0));
           first.append(l);
           second.insert(0, l);
       }
        System.out.println(((oddCnt == 1) ? (first.toString() + oddChar + second) : (first.toString() + second)));
    }
}