#define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
using namespace std;

int main() {
  string S; cin >> S;
  int s = (int)S.size();
  if(s%2 != 0){
    cout << "NO" << endl;
  }else{
    for(int i = 0; i < s/2; i++){
      if(S[i] != S[i+s/2]){
        cout << "NO" << endl;
        return 0;
      }
    }
    cout << "YES" << endl;
  }
}