#include <bits/stdc++.h>
using namespace std;
int main(){
  string s;
  cin >> s;
  if(s.size()%2==0 and s.substr(0,s.size()/2)==s.substr(s.size()/2,s.size()/2)){
    cout << "YES" << endl;
  }else{
    cout << "NO" << endl;
  }
  return 0;
}