//https://ncode.syosetu.com/n4830bu/238/
#include <bits/stdc++.h>
using namespace std;

int main() {
    string s;
    cin >> s;
    int l = 0, r = s.size() - 1;
    while (true) {
        if (s[l] != s[r])
            break;
        if (r - l <= 2) {
            if (s.size() % 2 == 0)
                cout << s.substr(0, l + 1) + "a" + s.substr(r, l + 1) << endl;
            else
                cout << s.substr(0, l + 1) + s[(l + 1)] + s[(l + 1)] + s.substr(r, l + 1) << endl;
            return 0;
        }
        l++;
        r--;
    }
    string t = s;
    t.insert(l, s.substr(r, 1));
    if (equal(t.begin(), t.end(), t.rbegin())) {
        cout << t << endl;
        return 0;
    }
    t = s;
    t.insert(r + 1, s.substr(l, 1));
    if (equal(t.begin(), t.end(), t.rbegin())) {
        cout << t << endl;
        return 0;
    }
    cout << "NA" << endl;
}