#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <vector>
#include <string>
#include <queue>
#include <algorithm>
#include <math.h>
#include <utility>
#include <set>
#include <map>
#include <cstring>
#include <cstdio>
#include <stack>
#include <cmath>
#define INF 10000000000
#define MOD 10000000007
#define rep(i,n) for(int i =0;i<n;i++)
using namespace std;
typedef long long int ll;
typedef pair<int, int> i_i;


int main(){
    string s;
    cin >> s;
    int ch = 0;
    string h=s;
    int a=0,b=s.length()-1;
    while(a<=b){
        if (s[a]==s[b]) {
            a++;
            b--;
            continue;
        }else{
            if (s[a+1]==s[b]) {
                h = h.substr(0,b+1)+s[a]+s.substr(b+1,s.length()-b);
                ch++;
                a++;
                continue;
            }
            if (s[a]==s[b-1]) {
                h = h.substr(0,a)+s[b]+s.substr(a,s.length()-a);
                ch++;
                b--;
                continue;
            }
            a++;
            b--;
            ch+=10;
        }
    }
    if (ch==1) {
        cout << h << endl;
        return 0;
    }
    if (ch == 0) {
        string ans = "";
        if (h.length()%2==0) {
            ans = h.substr(0,h.length()/2)+"a"+h.substr(h.length()/2,h.length()/2);
        }else{
            ans = h.substr(0,h.length()/2)+h[h.length()/2]+h.substr(h.length()/2+1,h.length()/2);
        }
        cout << ans << endl;
        return 0;
    }
    if(ch>1) cout << "NA" <<endl;
}