#include <bits/stdc++.h>

using namespace std;

bool isKaibun(string s) {
	int n = s.length();
	for (int i = 0; i < n / 2; i++) {
		if (s[i] != s[n - 1 - i]) return false;
	}
	return true;
}

int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	string s;
	cin >> s;
	int n = s.length();
	string c;
	if (isKaibun(s)) {
		c = s[n / 2];
		s.insert(n / 2, c);
		cout << s << endl;
		return 0;
	}
	int cnt = 0, idx = -1;
	for (int i = 0; i < (n - 1) / 2; i++) {
		cnt += (s[i] != s[n - 1 - i - cnt]);
		if (cnt > 1) break;
		if (cnt == 1 && idx == -1) {
			idx = i;
			c = s[n - 1 - i];
			i--;
		}
	}
	if (cnt == 0) {
		idx = (n - 1) / 2;
		c = s[n / 2];
	}
	if (cnt <= 1) {
		s.insert(idx, c);
		cout << s << endl;
		return 0;
	}

	cnt = 0;
	idx = -1;
	reverse(s.begin(), s.end());

	for (int i = 0; i < (n - 1) / 2; i++) {
		cnt += (s[i] != s[n - 1 - i - cnt]);
		if (cnt > 1) break;
		if (cnt == 1 && idx == -1) {
			idx = i;
			c = s[n - 1 - i];
			i--;
		}
	}
	if (cnt == 0) {
		idx = (n - 1) / 2;
		c = s[n / 2];
	}

	if (cnt <= 1) {
		s.insert(idx, c);
		cout << s << endl;
		return 0;
	}	

	cout << "NA" << endl;
	return 0;
}