#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
using ll = long long;
using u64 = uint_fast64_t;
using pii =  pair<int, int>;
using pll =  pair<long long, long long>;
#define rep(i, n) for(int i = 0; i < (n); ++i)
#define all(x) (x).begin(),(x).end()
constexpr char ln = '\n';
constexpr long long MOD = 1000000007;
//constexpr long long MOD = 998244353;
template<class T1, class T2> inline bool chmax(T1 &a, T2 b) { if (a < b) { a = b; return true;} return false; }
template<class T1, class T2> inline bool chmin(T1 &a, T2 b) { if (a > b) { a = b; return true;} return false; }
inline int popcount(int x) {return __builtin_popcount(x);}
inline int popcount(long long x) {return __builtin_popcountll(x);}
void print() { cout << "\n"; }
template<class T, class... Args>
void print(const T &x, const Args &... args) {
    cout << x << " ";
    print(args...);
}
///////////////////////////////////////////////////////////////////////////////////////////////////////////////

int main() {
    ios::sync_with_stdio(false); cin.tie(nullptr);
    string S; cin >> S;
    int N = S.size();

    deque<char> deq,L,R;
    rep(i,N) deq.emplace_back(S[i]);

    while ((int)deq.size() >= 2) {
        if (deq.front()==deq.back()) {
            L.emplace_back(deq.front());
            deq.pop_front();
            R.emplace_front(deq.back());
            deq.pop_back();
        } else {
            bool ok = true;
            {
                auto T = deq;
                T.emplace_front(T.back());
                auto LL = L;
                auto RR = R;
                while ((int)T.size() >= 2) {
                    if (T.front()==T.back()) {
                        LL.emplace_back(T.front());
                        T.pop_front();
                        RR.emplace_front(T.back());
                        T.pop_back();
                    } else {
                        ok = false;
                        break;
                    }      
                }
                if (ok) {
                    string ans = "";
                    while (!LL.empty()) {
                        ans += LL.front();
                        LL.pop_front();
                    }
                    while (!T.empty()) {
                        ans += T.front();
                        T.pop_front();
                    }
                    while (!RR.empty()) {
                        ans += RR.front();
                        RR.pop_front();
                    }

                    cout << ans << ln;
                    return 0;
                }
            }

            ok = true;

            {
                auto T = deq;
                T.emplace_back(T.front());
                auto LL = L;
                auto RR = R;
                while ((int)T.size() >= 2) {
                    if (T.front()==T.back()) {
                        LL.emplace_back(T.front());
                        T.pop_front();
                        RR.emplace_front(T.back());
                        T.pop_back();
                    } else {
                        ok = false;
                        break;
                    }      
                }
                if (ok) {
                    string ans = "";
                    while (!LL.empty()) {
                        ans += LL.front();
                        LL.pop_front();
                    }
                    while (!T.empty()) {
                        ans += T.front();
                        T.pop_front();
                    }
                    while (!RR.empty()) {
                        ans += RR.front();
                        RR.pop_front();
                    }

                    cout << ans << ln;
                    return 0;
                } else {
                    cout << "NA" << ln;
                    return 0;
                }
            }
        }
    }

    if (deq.empty()) {
        string ans = "";
        while (!L.empty()) {
            ans += L.front();
            L.pop_front();
        }
        ans += 'a';
        while (!R.empty()) {
            ans += R.front();
            R.pop_front();
        }

        cout << ans << ln;
    } else {
        string ans = "";
        while (!L.empty()) {
            ans += L.front();
            L.pop_front();
        }
        ans += deq.front();
        ans += deq.front();
        while (!R.empty()) {
            ans += R.front();
            R.pop_front();
        }

        cout << ans << ln;
    }
}