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

int main(){
  string s;
  cin >> s;

  if(s.size() % 2 != 0){
    cout << "NO" << endl;
    return 0;
  }

  for(int i = 0;i < s.size()/2;i++){
    if(s[i] != s[i+s.size()/2]){
      cout << "NO" << endl;
      return 0;
    }
  }

  cout << "YES" << endl;
  return 0;
}