#include <bits/stdc++.h>

int main() {

  std::string str;
  std::string str2;

  int p;
  char c;

  std::cin >> str;
  str2 = str;
  std::reverse(str2.begin(), str2.end());
  int n = str.size();

  for(int i = 0; i < str.size(); ++i) {
    if( str[i] != str2[i] ) {
      p = i;
      break;
    }
  }

  if( p > str.size()/2 ) {
    if( str.size() % 2 == 0 ) {
      std::stringstream ss;
      for(int i = 0; i < n/2; ++i) {
	ss << str[i];
      }
      ss << 'a';
      for(int i = n/2; i < n; ++i) {
	ss << str[i];
      }
      str = ss.str();
      str2 = str;
      std::reverse(str2.begin(), str2.end());
      if( str == str2 ) {
	std::cout << str << std::endl;
      }
      else {
	std::cout << "NA" << std::endl;
      }
      return 0;
    }
    else {
      std::cout << "NA" << std::endl;
      return 0;
    }
  }

  if( p != 0 ) {
    c = str[str.size()-p-1];
  }
  else {
    p = n;
    c = str[0];
  }
    
  std::stringstream ss;
  for(int i = 0; i < p; ++i) {
    ss << str[i];
  }
  ss << c;
  for(int i = p; i < n; ++i) {
    ss << str[i];
  }
  str = ss.str();
  str2 = str;
  std::reverse(str2.begin(), str2.end());
  if( str == str2 ) {
    std::cout << str << std::endl;
  }
  else {
    std::cout << "NA" << std::endl;
  }
  
  return 0;
}