using System;
using System.Linq;

class MainClass
{
    public static void Main(string[] args)
    {
        string s = Console.ReadLine();

        int[] cnt = new int[26];

        foreach (char c in s)
        {
            cnt[c - 'a']++;
        }

        int n = s.Length, mx = cnt.Max();
        char last = '-';

        if (2 * mx > n + 1)
        {
            Console.WriteLine("-1");
            return;
        }

        for (int i = 0; i < n; i++)
        {
            mx = cnt.Max();
            int secondMx = cnt.OrderByDescending(x => x).Skip(1).First();
            for (int j = 0; j < 26; j++)
            {
                if (last != (char)('a' + j) && cnt[j] > 0)
                {
                    if (mx == cnt[j] || mx <= (n - i - 1) / 2 && secondMx <= n - i - mx - 2)
                    {
                        Console.Write((char)('a' + j));
                        cnt[j]--;
                        last = (char)('a' + j);
                        break;
                    }
                }
            }
        }
    }
}