using System;
using System.IO;
using System.Linq;
using System.Text;
using System.Collections.Generic;
using System.Diagnostics;
using System.Numerics;
using Enu = System.Linq.Enumerable;

class Program
{
    static readonly string Bad = "NA";

    public void Solve()
    {
        string S = Reader.String();
        var ans = Rec(S, 0, S.Length - 1, false);
        if (S != Bad && ans == S)
            if (ans.Length % 2 == 0) ans = ans.Insert(ans.Length / 2, "a");
            else ans = ans.Insert(ans.Length / 2, ans[ans.Length / 2] + "");
        Console.WriteLine(ans);
    }

    string Rec(string S, int L, int R, bool inserted)
    {
        if (L >= R) return S;
        if (S[L] == S[R]) return Rec(S, L + 1, R - 1, inserted);
        if (inserted) return Bad;
        var insertL = Rec(S.Insert(L, S[R] + ""), L + 1, R, true);
        if (insertL != Bad) return insertL;
        return Rec(S.Insert(R + 1, S[L] + ""), L + 1, R, true);
    }
}



class Entry { static void Main() { new Program().Solve(); } }
class Reader
{
    private static TextReader reader = Console.In;
    private static readonly char[] separator = { ' ' };
    private static readonly StringSplitOptions op = StringSplitOptions.RemoveEmptyEntries;
    private static string[] A = new string[0];
    private static int i;
    private static void Init() { A = new string[0]; }
    public static void Set(TextReader r) { reader = r; Init(); }
    public static void Set(string file) { reader = new StreamReader(file); Init(); }
    public static bool HasNext() { return CheckNext(); }
    public static string String() { return Next(); }
    public static int Int() { return int.Parse(Next()); }
    public static long Long() { return long.Parse(Next()); }
    public static double Double() { return double.Parse(Next()); }
    public static int[] IntLine() { return Array.ConvertAll(Split(Line()), int.Parse); }
    public static int[] IntArray(int N) { return Enu.Range(0, N).Select(i => Int()).ToArray(); }
    public static int[][] IntTable(int H) { return Enu.Range(0, H).Select(i => IntLine()).ToArray(); }
    public static string[] StringArray(int N) { return Enu.Range(0, N).Select(i => Line()).ToArray(); }
    public static string Line() { return reader.ReadLine().Trim(); }
    private static string[] Split(string s) { return s.Split(separator, op); }
    private static string Next() { CheckNext(); return A[i++]; }
    private static bool CheckNext()
    {
        if (i < A.Length) return true;
        string line = reader.ReadLine();
        if (line == null) return false;
        if (line == "") return CheckNext();
        A = Split(line);
        i = 0;
        return true;
    }
}