using System;
using System.Linq;

namespace Yuki
{
    class Program
    {
        static void Main(string[] args)
        {
            string s = Console.ReadLine();
            int i = 0;
            int j = s.Length - 1;
            int c = -1;
            int d = -1;

            bool f = true;
            while (i <= j)
            {
                if (s[i] != s[j])
                {
                    c = i;
                    d = j;
                    f = false;
                    break;
                }
                i++;
                j--;
            }

            if (f)
            {
                Console.Write(s.Insert(s.Length / 2, s[s.Length / 2].ToString()));
            }
            else
            {
                string a = s.Insert(c, s[d].ToString());
                string b = s.Insert(d, s[c].ToString());
                string a2 = new string(a.Reverse().ToArray());
                string b2 = new string(b.Reverse().ToArray());


                if (a == a2)
                {
                    Console.WriteLine(a);
                }
                else if (b == b2)
                {
                    Console.WriteLine(b);
                }
                else
                {
                    Console.WriteLine("NA");
                }
            }
        }
    }
}