#include <bits/stdc++.h>
#define rep(i, a) for (int i = 0; i < (a); i++)
#define rep2(i, a, b) for (int i = (a); i < (b); i++)
using namespace std;
typedef long long ll;
const ll inf = 1e9;
const ll mod = 1e9 + 7;

bool pal(string s) {
    rep (i, s.length()) {
        if (s[i] != s[s.length() - i - 1]) {
            return false;
        }
    }
    return true;
}

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

    if (pal(s)) {
        if (s.length() % 2 == 0) {
            s.insert(s.length() / 2, "a");
        } else {
            s.insert(s.length() / 2, string(1, s[s.length() / 2]));
        }

        cout << s << endl;
        return 0;
    }

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

    vector<int> diff(s.length());

    rep (i, s.length()) {
        diff[i] = s[i] - t[i];
    }

    int pos = 0;

    rep (i, s.length()) {
        if (diff[i] != 0) {
            pos = i;
            break;
        }
    }

    string u = s[s.length() - 1] + s;

    t += "~";

    for (int i = t.length() - 1; i > pos; i--) {
        t[i] = t[i - 1];
    }

    t[pos] = t[t.length() - pos - 1];

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