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

typedef unsigned long long Hash;
template<class T>
class RollingHash{
public:
	T src;
	vector<Hash> harr,p;
	
	vector<int> suffixArray;
	RollingHash(T src,Hash w=8999):src(src){
		p.resize(src.size()+10);
		Hash sum = 0;
		for(int i = 0 ; i < src.size() ; i++){
			sum = sum * w + src[i];
			harr.push_back(sum);
		}
		p[0] = 1;
		for(int i = 1 ; i < p.size() ; i++){
			p[i] = p[i-1] * w;
		}
	}
	Hash sub(int l,int r) const{
		if( l >= r ) return 0;
		return harr[r-1] - (l?harr[l-1] * p[r-l]:0);
	}
	Hash merge(Hash a,Hash b,int blen){
		return a * p[blen] + b;
	}
};
int assign[128] = {};

int main(){
	for(int i = 0 ; i < 128 ; i++) assign[i] = i;
	random_shuffle(assign,assign+128);
	string s,src;
	cin >> s;
	src = s;
	for(int i = 0 ; i < s.size() ; i++) 
		s[i] = assign[s[i]];
	RollingHash<string> fr(s);
	reverse(s.begin(),s.end());
	RollingHash<string> bk(s);
	reverse(s.begin(),s.end());
	
	
	for(int i = 0 ; i <= s.size() ; i++){
		for(int j = 0 ; j < 26 ; j++){
			char ins = assign['a'+j];
			Hash frA = fr.sub(0,i);
			Hash frB = fr.sub(i,s.size());
			Hash frR = fr.merge(fr.merge(frA,ins,1),frB,s.size()-i);
			
			Hash bkA = bk.sub(0,s.size()-i);
			Hash bkB = bk.sub(s.size()-i,s.size());
			
			Hash bkR = bk.merge(bk.merge(bkA,ins,1),bkB,i);
			if( bkR == frR ){
				cout << src.substr(0,i) + string(1,j + 'a') + src.substr(i) << endl;
				return 0;
			}
		}
	}
	cout << "NA" << endl;
	
	
	
}