#include <iostream>
#include <sstream>
#include <string>
#include <vector>
#include <functional>
#include <tuple>
#include <climits>
#include <algorithm>
#include <queue>
#include <unordered_map>
#include <unordered_set>
#include <set>
#include <numeric>
#include <map>
#include <cmath>
#include <cstdlib>
#include <iomanip>

using namespace std;

bool solve(string s, int count)
{
    bool success = true;
    for(int i=0; i<s.size()/2; i++) {
        if(s[i] == s[s.size()-i-1]) continue;
        else {
            success = false;
            if(count == 1) return false;
            string s1=s, s2=s;
            s1.insert(i, 1, s[s.size()-i-1]);
            s2.insert(s.size()-i, 1, s[i]);
            if(solve(s1, 1) || solve(s2, 1) ) return true;
            cout << "NA" << endl;
            return false;
        }
    }
    if(success) {
        if(count == 0 && s.size()%2 == 0) {
            s.insert(s.size()/2, 1, 'a');
        }
        cout << s << endl;
    }

    return true;
}

int main()
{
    string s;
    cin >> s;
    solve(s, 0);
}