#include<iostream>
#include<cstdio>
#include<vector>
#include<queue>
#include<map>
#include<string>
#include<algorithm>
#include<functional>
using namespace std;
#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define RFOR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n) for (int i=0;i<(n);i++)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)
#define INF 1<<30
#define MP make_pair
#define mp make_pair
#define pb push_back
#define PB push_back
#define DEBUG(x) cout<<#x<<": "<<x<<endl
#define ll long long
#define ull unsigned long long

void strreverse(string& a){
	string tmp=a;
	REP(i,a.size()){
		a[i]=tmp[a.size()-i-1];
		
	}
}

int main(){
	string s;
	cin>>s;
	int cnt=0;
	int ini=0;
	bool f=false;
	string str=s;
	REP(i,(1+s.size())/2){
		if(s[i]==s[s.size()-i-1+cnt]) continue;
		cnt++;ini=i;
	}
	if(cnt<=1){
		f=true;
		if(cnt==1) str.insert(s.size()-ini,1,s[ini]);
		else if(s.size()%2){
			str.insert(s.size()/2,1,s[s.size()/2]);
		}else {
			str.insert(s.size()/2,1,'a');
		}
		cout<<str<<endl;return 0;
	}
	cnt=0;
	strreverse(s);
	strreverse(str);
	REP(i,(1+s.size())/2){
		if(s[i]==s[s.size()-i-1+cnt]) continue;
		cnt++;ini=i;
	}
	if(cnt<=1){
		f=true;
		if(cnt==1) str.insert(s.size()-ini,1,s[ini]);
		else if(s.size()%2){
			str.insert(s.size()/2,1,s[s.size()/2]);
		}else {
			str.insert(s.size()/2,1,'a');
		}
		cout<<str<<endl;return 0;
	}
	cout<<"NA"<<endl;
	return 0;
}