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 - 1, 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; } }