#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <iomanip>
#include <cmath>
#include <stdio.h>
#include <queue>
#include <deque>
#include <cstdio>
#include <set>
#include <map>
#include <bitset>
#include <stack>
#include <cctype>
using namespace std;
int main() {
	string s;
	cin >> s;
	int n = s.size();
	if (n % 2 == 0) {
		string s1 = s.substr(0, n / 2);
		string t1 = s.substr(n / 2 + 1, n / 2 - 1);
		reverse(t1.begin(), t1.end());
		string t2 = s.substr(0, n / 2 - 1);
		string s2 = s.substr(n / 2, n / 2);
		reverse(s2.begin(), s2.end());
		bool bo = false, bo1 = true;
		for (int i = 0; i < s1.size(); i++) {
			if ((!bo & (i == s1.size() - 1)) || (!bo & s1[i] != t1[i - bo])) {
				bo = true;
				continue;
			}
			else if (s1[i] != t1[i - bo]) {
				bo1 = false;
				break;
			}
		}
		if (bo1) {
			cout << s1 << s[n / 2];
			reverse(s1.begin(), s1.end());
			cout << s1 << endl;
			return 0;
		}
		bo = false, bo1 = true;
		for (int i = 0; i < s2.size(); i++) {
			if ((!bo & (i == s2.size() - 1)) || (!bo & s2[i] != t2[i - bo])) {
				bo = true;
				continue;
			}
			else if (s2[i] != t2[i - bo]) {
				bo1 = false;
				break;
			}
		}
		if (bo1) {
			cout << s2 << s[n / 2 - 1];
			reverse(s2.begin(), s2.end());
			cout << s2 << endl;
			return 0;
		}
		if (s1 == s2) {
			cout << s1 << 'a';
			reverse(s1.begin(), s1.end());
			cout << s1 << endl;
			return 0;
		}
		cout << "NA" << endl;
		return 0;
	}
	else {
		string s1 = s.substr(0, n / 2 + 1);
		string t1 = s.substr(n / 2 + 1, n / 2);
		reverse(t1.begin(), t1.end());
		string t2 = s.substr(0, n / 2);
		string s2 = s.substr(n / 2, n / 2 + 1);
		reverse(s2.begin(), s2.end());
		bool bo = false, bo1 = true;
		for (int i = 0; i < s1.size(); i++) {
			if ((!bo & (i == s1.size() - 1)) || (!bo & s1[i] != t1[i - bo])) {
				bo = true;
				continue;
			}
			else if (s1[i] != t1[i - bo]) {
				bo1 = false;
				break;
			}
		}
		if (bo1) {
			cout << s1;
			reverse(s1.begin(), s1.end());
			cout << s1 << endl;
			return 0;
		}
		bo = false, bo1 = true;
		for (int i = 0; i < s2.size(); i++) {
			if ((!bo & (i == s2.size() - 1)) || (!bo & s2[i] != t2[i - bo])) {
				bo = true;
				continue;
			}
			else if (s2[i] != t2[i - bo]) {
				bo1 = false;
				break;
			}
		}
		if (bo1) {
			cout << s2;
			reverse(s2.begin(), s2.end());
			cout << s2 << endl;
			return 0;
		}
		if (s1 == s2) {
			cout << s1;
			reverse(s1.begin(), s1.end());
			cout << s1 << endl;
			return 0;
		}
		cout << "NA" << endl;
		return 0;
	}
}