/* -*- coding: utf-8 -*-
 *
 * 238.cc: No.238 Mr. K's Another Gift - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

/* typedef */

/* global variables */

/* subroutines */

/* main */

int main() {
  string s;
  cin >> s;
  int n = s.size();

  int l = 0, r = n - 1;
  while (l < r && s[l] == s[r]) l++, r--;
  //printf("l=%d, r=%d\n", l, r);

  if (l >= r) {
    if (l == r) {
      for (int i = 0; i <= l; i++) putchar(s[i]);
      for (int i = r; i < n; i++) putchar(s[i]);
      putchar('\n');
    }
    else {
      for (int i = 0; i < l; i++) putchar(s[i]);
      putchar('a');
      for (int i = r + 1; i < n; i++) putchar(s[i]);
      putchar('\n');
    }
    return 0;
  }

  int l0 = l + 1, r0 = r;
  while (l0 < r0 && s[l0] == s[r0]) l0++, r0--;
  if (l0 >= r0) {
    for (int i = 0; i <= r; i++) putchar(s[i]);
    putchar(s[l]);
    for (int i = r + 1; i < n; i++) putchar(s[i]);
    putchar('\n');
    return 0;
  }

  l0 = l, r0 = r - 1;
  while (l0 < r0 && s[l0] == s[r0]) l0++, r0--;
  if (l0 >= r0) {
    for (int i = 0; i < l; i++) putchar(s[i]);
    putchar(s[r]);
    for (int i = l; i < n; i++) putchar(s[i]);
    putchar('\n');
    return 0;
  }

  puts("NA");
  return 0;
}