#include<iostream>
#include<cstdlib>
#include<string>

int main() {
  std::string S;
  std::cin >> S;
  int length = S.size();

  if(length%2 == 0) {
    std::string Sa, Sb; 
    Sa = S.substr(0,length/2);
    Sb = S.substr(length/2, length/2);
    if(Sa == Sb) {
      std::cout << "YES" << std::endl; 
    } else {
      std::cout << "NO" << std::endl;
    }
  } else {
    std::cout << "NO" << std::endl;
  }
  
}