#include <iostream>
#include <vector>
#include <cstdio>
#include <sstream>
#include <map>
#include <string>
#include <algorithm>
#include <queue>
#include <cmath>
#include <set>
using namespace std;

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

	string r = s;
	reverse(r.begin(), r.end());

	bool valid = true;
	int pos = -1;
	for(int i=0; i<n; i++){
		if(r[i] != s[i]){
			valid = false;
			pos = i;
			break;
		}
	}

	if(valid){
		if(n%2 == 0){
			cout << s.substr(0, n/2) << "a" << s.substr(n/2, n/2) << endl;
		}else{
			string sub_a = s.substr(0, n/2);
			string sub_b = r.substr(0, n/2);
			if(sub_a == sub_b){
				string t = sub_a;
				t += s[n/2];
				t += s[n/2];
				reverse(sub_a.begin(), sub_a.end());
				t += sub_a;
				cout << t << endl;
			}else{
				cout << "NA" << endl;
			}
		}
		return 0;
	}

	string t = r.substr(0, pos);
	t += s[pos];
	t += r.substr(pos, string::npos);

	r = t;
	reverse(r.begin(), r.end());

	valid = true;
	for(int i=0; i<t.size(); i++){
		if(r[i] != t[i]){
			valid = false;
			break;
		}
	}

	if(valid){
		cout << t << endl;
	}else{
		r = s;
		reverse(s.begin(), s.end());
		bool valid = true;

		int pos = -1;
		for(int i=0; i<n; i++){
			if(r[i] != s[i]){
				valid = false;
				pos = i;
				break;
			}
		}

		if(valid){
			if(n%2 == 0){
				cout << s.substr(0, n/2) << "a" << s.substr(n/2, n/2) << endl;
			}else{
				cout << "NA" << endl;
			}
			return 0;
		}

		string t = r.substr(0, pos);
		t += s[pos];
		t += r.substr(pos, string::npos);

		r = t;
		reverse(r.begin(), r.end());

		valid = true;
		for(int i=0; i<t.size(); i++){
			if(r[i] != t[i]){
				valid = false;
				break;
			}
		}

		if(valid){
			cout << t << endl;
		}else cout << "NA" << endl;
	}

	return 0;
}