using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Váltakozó_szöveg{
    class Program{
        static void Main(){
            string str = Console.ReadLine();
            int[] a = new int[26];
            string o = "";
            foreach (char i in str) a[i - 'a']++;
            int n = str.Length;
            int m = a.Max();
            char last = '-';
            if (2 * m > n + 1){
                Console.WriteLine("-1");
                return;
            }
            while (n >= 1){
                m = a.Max();
                for(int i=0; i<26; i++){
                    if(last!=i+'a'&& a[i]>0 && (2*m<=n || m == a[i])){
                        o += (last = (char)(i + 'a'));
                        a[i]--;
                        break;
                    }
                }
            }
            Console.WriteLine(o);
        }
    }
}