import std.algorithm, std.array, std.container, std.range, std.bitmanip;
import std.numeric, std.math, std.bigint, std.random, core.bitop;
import std.string, std.regex, std.conv, std.stdio, std.typecons;

void main()
{
  auto s = readln.chomp;

  writeln(calc(s));
}

string calc(string s)
{
  foreach (i; 0..s.length/2) {
    if (s[i] != s[$-i-1]) {
      auto s2 = s[$-i-1] ~ s[i..$-i];
      if (isKaibun(s2))
        return s[0..i] ~ s2 ~ s[$-i..$];
      auto s3 = s[i..$-i] ~ s[i];
      if (isKaibun(s3))
        return s[0..i] ~ s3 ~ s[$-i..$];
      return "NA";
    }
  }

  if (s.length % 2 == 0)
    return s[0..s.length/2] ~ "a" ~ s[s.length/2..$];
  else
    return s[0..s.length/2] ~ s[s.length/2] ~ s[s.length/2] ~ s[s.length/2+1..$];
}

bool isKaibun(string s)
{
  foreach (i; 0..s.length/2)
    if (s[i] != s[$-i-1]) return false;
  return true;
}