import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintStream;
import java.io.PrintWriter;
import java.util.ArrayDeque;
import java.util.Arrays;
import java.util.Iterator;
import java.util.Queue;


public class Main_yukicoder238 {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        Printer pr = new Printer(System.out);

        char[] s = sc.next().toCharArray();
        int n = s.length;

        Queue<Character> fq = new ArrayDeque<Character>();
        Queue<Character> rq = new ArrayDeque<Character>();
        boolean flag = false;
        for (int i = 0; i < n; i++) {
    		if (!flag && s[i] != s[n - 1 - i]) {
    			rq.add(s[i]);
    			fq.add(s[n - 1 - i]);
    			flag = true;
    		}
    		fq.add(s[i]);
    		rq.add(s[n - 1 - i]);
        }

        if (!flag) {
        	StringBuilder ret = new StringBuilder();
        	int len = (n + 1) / 2;
        	for (int i = 0; i < len; i++) {
        		ret.append(s[i]);
        	}
        	ret.append(s[len - 1]);
        	for (int i = len; i < n; i++) {
        		ret.append(s[i]);
        	}
        	
        	pr.println(ret);
        } else {
        	Character[] tmp = new Character[0];
        	tmp = fq.toArray(tmp);
        	boolean res = true;
            for (int i = 0; i < tmp.length; i++) {
            	if (tmp[i] != tmp[tmp.length - 1 - i]) {
            		res = false;
            		break;
            	}
            }
            
            if (res) {
            	StringBuilder ret = new StringBuilder();
            	for (int i = 0; i < tmp.length; i++) {
            		ret.append(tmp[i]);
            	}
            	
            	pr.println(ret);

            	pr.close();
            	sc.close();
            	
            	return;
            }

        	Character[] tmp2 = new Character[0];
        	tmp2 = rq.toArray(tmp2);
        	boolean res2 = true;
            for (int i = 0; i < tmp2.length; i++) {
            	if (tmp2[i] != tmp2[tmp2.length - 1 - i]) {
            		res2 = false;
            		break;
            	}
            }
            
            if (res2) {
            	StringBuilder ret = new StringBuilder();
            	for (int i = 0; i < tmp2.length; i++) {
            		ret.append(tmp2[i]);
            	}
            	
            	pr.println(ret);
            } else {
            	pr.println("NA");
            }
        }

        pr.close();
        sc.close();
    }

	@SuppressWarnings("unused")
	private static class Scanner {
		BufferedReader br;
		Iterator<String> it;
		
		Scanner (InputStream in) {
			br = new BufferedReader(new InputStreamReader(in));
		}
		
		String next() throws RuntimeException  {
			try {
				if (it == null || !it.hasNext()) {
					it = Arrays.asList(br.readLine().split(" ")).iterator();
				}
				return it.next();
			} catch (IOException e) {
				throw new IllegalStateException();
			}
		}
		
		int nextInt() throws RuntimeException {
			return Integer.parseInt(next());
		}

		long nextLong() throws RuntimeException {
			return Long.parseLong(next());
		}

		float nextFloat() throws RuntimeException {
			return Float.parseFloat(next());
		}

		double nextDouble() throws RuntimeException {
			return Double.parseDouble(next());
		}

		void close() {
			try {
				br.close();
			} catch (IOException e) {
//				throw new IllegalStateException();
			}
		}
	}

	private static class Printer extends PrintWriter {
		Printer(PrintStream out) {
			super(out);
		}
	}
}