#include "bits/stdc++.h"
using namespace std;

#define REP(i, n) for(int i=0; i<(n); i++)

signed main()
{
    string s;
    cin >> s;
    int f = 0;
    int t = s.size() - 1;
    bool ok = true;
    bool insert = false;
    while(f <= t) {
        if (s[f] != s[t]) {
            if (insert) {
                ok = false;
                break;
            } else if (s[f] == s[t-1]) {
                s.insert(f, s.substr(t, 1).c_str());
                insert = true;
                t++;
            } else if (s[f+1] == s[t]) {
                s.insert(t+1, s.substr(f, 1).c_str());
                insert = true;
                t++;
            } else {
                ok = false;
                break;
            }
        }
        f++;
        t--;
    }
    if (ok && !insert) {
        int t = s.size() / 2;
        s.insert(t, s.substr(t, 1).c_str());
    }
    cout << (ok ? s : "NA") << endl;
    return 0;
}