# include "bits/stdc++.h"
using namespace std;
using LL = long long;
using ULL = unsigned long long;
const double PI = acos(-1);
template<class T>constexpr T INF() { return ::std::numeric_limits<T>::max(); }
template<class T>constexpr T HINF() { return INF<T>() / 2; }
template <typename T_char>T_char TL(T_char cX) { return tolower(cX); };
template <typename T_char>T_char TU(T_char cX) { return toupper(cX); };
const int vy[] = { -1, -1, -1, 0, 1, 1, 1, 0 }, vx[] = { -1, 0, 1, 1, 1, 0, -1, -1 };
const int dx[4] = { -1,0,1,0 }, dy[4] = { 0,-1,0,1 };
int popcnt(unsigned long long n) { int cnt = 0; for (int i = 0; i < 64; i++)if ((n >> i) & 1)cnt++; return cnt; }
int d_sum(LL n) { int ret = 0; while (n > 0) { ret += n % 10; n /= 10; }return ret; }
int d_cnt(LL n) { int ret = 0; while (n > 0) { ret++; n /= 10; }return ret; }
LL gcd(LL a, LL b) { if (b == 0)return a; return gcd(b, a%b); };
LL lcm(LL a, LL b) { LL g = gcd(a, b); return a / g*b; };
# define ALL(qpqpq)           (qpqpq).begin(),(qpqpq).end()
# define UNIQUE(wpwpw)        (wpwpw).erase(unique(ALL((wpwpw))),(wpwpw).end())
# define LOWER(epepe)         transform(ALL((epepe)),(epepe).begin(),TL<char>)
# define UPPER(rprpr)         transform(ALL((rprpr)),(rprpr).begin(),TU<char>)
# define FOR(i,tptpt,ypypy)   for(LL i=(tptpt);i<(ypypy);i++)
# define REP(i,upupu)         FOR(i,0,upupu)
# define INIT                 std::ios::sync_with_stdio(false);std::cin.tie(0)
# pragma warning(disable:4996)

string s;
bool inserted;
bool b;
char c;
int pos;
int main() {
	cin >> s;
	REP(i, s.size() / 2) {
		if (s[i + (inserted && !b ? 1 : 0)] != s[s.size() - i - 1 - (inserted && b ? 1 : 0)]) {
			if (inserted) {
				cout << "NA" << endl;
				return 0;
			}
			if (s[i + 1] == s[s.size() - i - 1]) {
				pos = s.size() - i - 1;
				c = s[i];
				inserted = true;
				b = 0;
			}
			else if (s[i] == s[s.size() - i - 2]) {
				pos = i;
				c = s[s.size() - i - 1];
				inserted = true;
				b = 1;
			}
			else {
				cout << "NA" << endl;
				return 0;
			}
		}
	}
	if (!inserted) {
		pos = s.size() / 2;
		b = (s.size() % 2 ? 0 : 1);
		c = (s.size() % 2 ? s[s.size() / 2] : 'a');
	}
	REP(i, s.size()) {
		if (pos == i && b)cout << c;
		cout << s[i];
		if (pos == i && !b)cout << c;
	}
	cout << endl;
	//system("pause");
}