#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++)
#define repr(i, a) for (int i = (a) - 1; i >= 0; i--)
#define repr2(i, a, b) for (int i = (b) - 1; i >= (a); i--)
using namespace std;
typedef long long ll;
const ll inf = 1e9;
const ll mod = 1e9 + 7;

typedef unsigned long long ull;

const ull B = 1e8 + 7;

// abcde
// 12345
// edcbxa

ull sh[200000], th[200000];
ull pb[200000];

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

    int l = s.length();

    pb[0] = 1;
    rep (i, l) {
        pb[i + 1] = pb[i] * B;
    }

    rep (i, l) {
        sh[i + 1] = sh[i] + s[i] * pb[i];
        th[i + 1] = th[i] + t[i] * pb[i];
    }

    rep (i, l + 1) {
        rep (j, 26) {
            char ch = 'a' + j;
            ull ssh = sh[i] + ch * pb[i] + (sh[l] - sh[i]) * B;
            int k = l - i;
            ull tth = th[k] + ch * pb[k] + (th[l] - th[k]) * B;

            if (ssh == tth) {
                s.insert(i, 1, ch);
                return s;
            }
        }
    }

    return "NA";
}

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

    cout << solve(s) << endl;
}