#include<bits/stdc++.h>
using namespace std;
using Int = long long;
template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;}
template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;}


struct RollingHash{
  using ull = unsigned long long;
  vector<ull> hash,p;
  RollingHash(){}
  RollingHash(const string &s,ull B=1000000007LL){
    int n=s.size();
    hash.assign(n+1,0);
    p.assign(n+2,1);
    for(int i=0;i<n;i++){
      hash[i+1]=hash[i]*B+s[i];
      p[i+1]=p[i]*B;
    }
    p[n+1]=p[n]*B;
  }
  //S[l, r)
  ull find(int l,int r){
    return hash[r]-hash[l]*p[r-l];
  }
};

//INSERT ABOVE HERE
signed main(){
  string s;
  cin>>s;
  int n=s.size();
  string t(s);
  reverse(t.begin(),t.end());

  RollingHash rs(s),rt(t);
  for(int i=0;i<=n;i++){
    using ull = RollingHash::ull;
    for(int j='a';j<='z';j++){
      ull A=rs.find(0,i)*rs.p[n-i+1]+(j*rs.p[n-i])+rs.find(i,n);
      ull B=rt.find(0,n-i)*rt.p[i+1]+(j*rt.p[i])+rt.find(n-i,n);
      if(A==B){
        cout<<s.substr(0,i)<<char(j)<<s.substr(i,n)<<endl;
        exit(0);
      }
    }
  }
  cout<<"NA"<<endl;
  return 0;
}