#include <cstdio>
#include <iostream>
#include <vector>
#include <map>
#include <set>
#include <string>
#include <cstring>
#include <sstream>
#include <algorithm>
#include <functional>
#include <queue>
#include <stack>
#include <cmath>
#include <iomanip>
#include <list>
#include <tuple>
#include <bitset>
#include <ciso646>

using namespace std;

inline bool cheak(int x, int y, int xMax, int yMax){ return x >= 0 && y >= 0 && xMax > x && yMax > y; }
inline int toInt(string s) { int v; istringstream sin(s); sin >> v; return v; }
template<class T> inline string toString(T x) { ostringstream sout; sout << x; return sout.str(); }
template<class T> inline T sqr(T x) { return x*x; }

typedef pair<int, int> P;
typedef tuple<int, int, int> T;
typedef long long ll;
typedef unsigned long long ull;

#define For(i,a,b)	for(int (i) = (a);i < (b);(i)++)
#define rep(i,n)	For(i,0,n)
#define clr(a)		memset((a), 0 ,sizeof(a))
#define mclr(a)		memset((a), -1 ,sizeof(a))
#define all(a)		(a).begin(),(a).end()
#define sz(a)		(sizeof(a))
#define Fill(a,v)	fill((int*)a,(int*)(a+(sz(a)/sz(*(a)))),v)

const int dx[8] = { 1, 0, -1, 0, 1, 1, -1, -1 }, dy[8] = { 0, -1, 0, 1, -1, 1, -1, 1 };
const int mod = 1000000007;
const int INF = 1e9;


bool ok(string &s){
	int c = -1;
	rep(i, s.size() / 2){
		int t = s.size() - 1 - i;
		if (s[i] != s[t]){
			if (s[i] == '?'){ s[i] = s[t]; c = i; continue; }
			if (s[t] == '?'){ s[t] = s[i]; c = t; continue; }
			if(c != -1)s[c] = '?';
			return false;
		}
	}
	return true;
}

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

	bool f = true;
	rep(i, s.size() / 2){
		int t = s.size() - 1 - i;
		string ts;
		if (s[i] != s[t]){
			if (ok(ts = s.substr(0, i) + "?" + s.substr(i)) ||
				ok(ts = s.substr(0, i + 1) + "?" + s.substr(i + 1)) ||
				ok(ts = s.substr(0, t) + "?" + s.substr(t)) ||
				ok(ts = s.substr(0, t + 1) + "?" + s.substr(t + 1))){
				cout << ts << endl; return 0;
			}
			f = false;
			break;
		}
	}

	if (f){
		cout << s.substr(0, s.size() / 2) + s[s.size() / 2] + s.substr(s.size() / 2) << endl;
	}
	else{
		cout << "NA" << endl;
	}
	return 0;
}