#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <complex>
#include <queue>
#include <set>
#include <map>

using namespace std;

#define REP(i,a,b) for(int i=a;i<(int)b;i++)
#define rep(i,n) REP(i,0,n)

typedef long long ll;

int N;
string s;
string ans;

bool dfs(int a, int b, bool used) {

  if( (N+used) % 2 == 0 && a - 1 == b ) {
    string t = ans; reverse(t.begin(), t.end());
    string u = !used ? "x" : "";
    ans = ans + u + t;
    return true;
  }
  if( (N+used) % 2 == 1 && a - 2 == b ) {
    string t = ans; reverse(t.begin(), t.end());
    string u = !used ? "x" : "";
    ans = ans + u + t.substr(1);
    return true;
  }

  if(s[a] == s[b]) {
    ans += s[a];
    if(dfs(a+1, b-1, used)) { return true; }
    ans.pop_back();
  }
  else if(!used) {
    ans += s[a];
    if(dfs(a+1, b, true)) { return true; }
    ans.back() = s[b];
    if(dfs(a, b-1, true)) { return true; }
    ans.pop_back();
  }
  return false;
}

int main() {

  cin >> s;
  N = s.size();
  if(N == 1) {
    ans = s + s;
  }
  else {
    dfs(0, N-1, false);
  }
  if(ans.empty()) {
    cout << "NA\n";
  }
  else {
    cout << ans << endl;
  }

  return 0;
}