#define _CRT_SECURE_NO_WARNINGS
//#define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
//#define int ll
//#define endl "\n"
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int,int> pii;
#define all(c) (c).begin(), (c).end()
#define loop(i,a,b) for(ll i=a; i<ll(b); i++)
#define rep(i,b) loop(i,0,b)
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define mt make_tuple
template<class T> ostream & operator<<(ostream & os, vector<T> const &);
template<int n, class...T> typename enable_if<(n>=sizeof...(T))>::type _ot(ostream &, tuple<T...> const &){}
template<int n, class...T> typename enable_if<(n< sizeof...(T))>::type _ot(ostream & os, tuple<T...> const & t){ os << (n==0?"":" ") << get<n>(t); _ot<n+1>(os, t); }
template<class...T> ostream & operator<<(ostream & os, tuple<T...> const & t){ _ot<0>(os, t); return os; }
template<class T, class U> ostream & operator<<(ostream & os, pair<T,U> const & p){ return os << "(" << p.first << ", " << p.second << ") "; }
template<class T> ostream & operator<<(ostream & os, vector<T> const & v){ rep(i,v.size()) os << v[i] << (i+1==(int)v.size()?"":" "); return os; }
template<class T> inline bool chmax(T & x, T const & y){ return x<y ? x=y,true : false; }
template<class T> inline bool chmin(T & x, T const & y){ return x>y ? x=y,true : false; }
#ifdef DEBUG
#define dump(...) (cerr<<#__VA_ARGS__<<" = "<<mt(__VA_ARGS__)<<" ["<<__LINE__<<"]"<<endl)
#else
#define dump(...)
#endif

/*
  aaabbcaaa
 */

bool solve2(string s){
    int n = s.size();
    rep(i,n) if(s[i]!=s[n-i-1]) return false;
    return true;
}

string solve(string s){
    int n = s.size();
    int l = 0;
    int r = n-1;
    while(l < r && s[l] == s[r]) l++, r--;
    if(l >= r){
        if(n&1) return "";
        return s.substr(0,n/2) + 'a' + s.substr(n-n/2);
    } else {
        int len = r-l+2;
        string x = s[r] + s.substr(l,len);
        string y = s.substr(l,len) + s[l];
        if(solve2(x)) return x;
        if(solve2(y)) return y;
        return "";
    }
}

signed main(){
    ios_base::sync_with_stdio(0); cin.tie(0);
    string n;
    while(cin >> n){
        string ans = solve(n);
        if(ans.size()==0) puts("NA");
        else cout << ans << endl;
    }
}