#include <bits/stdc++.h>
using namespace std;
using i64 = int64_t;
using vi = vector<i64>;
using vvi = vector<vi>;

int main() {
    string s;
    cin >> s;

    if (s.size() == 1) {
        cout << s.front() << s.front() << endl;
        return 0;
    }
    deque<char> hoge;
    for (char c: s) {
        hoge.push_back(c);
    }

    string pref;
    while (hoge.size() > 1 && hoge.front() == hoge.back()) {
        pref.push_back(hoge.front());
        hoge.pop_front();
        hoge.pop_back();
    }
    string suf(pref);
    reverse(suf.begin(), suf.end());

    if (hoge.size() == 1) {
        cout << pref << hoge.front() << hoge.front() << suf << endl;
        return 0;
    } else if (hoge.empty()) {
        cout << pref << "a" << suf << endl;
        return 0;
    }

    deque<char> fuga(hoge), piyo(hoge);
    fuga.push_back(hoge.front());
    piyo.push_front(hoge.back());

    auto tostr = [](deque<char> d) {
        string ret = "";
        for (char c: d) {
            ret += c;
        }
        return ret;
    };

    string sf = tostr(fuga), sp = tostr(piyo);

    auto ok = [](string t) {
        string u(t);
        reverse(u.begin(), u.end());
        return t == u;
    };

    if (ok(sf)) {
        cout << pref << sf << suf << endl;
        return 0;
    } else if (ok(sp)) {
        cout << pref << sp << suf << endl;
        return 0;
    }

    cout << "NA" << endl;
}