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

int main(){
  string S;
  cin>>S;
  int len=S.length();
  if(len%2 != 0){
    cout<<"NO"<<endl;
    return 0;
  }
  if(S.substr(0,len/2)==S.substr(len/2,len/2)){
    cout<<"YES"<<endl;
  }
  else{
    cout<<"NO"<<endl;
  }
  //cout<<S.substr(0,len/2)<<" "<<S.substr(len/2,len/2)<<endl;
}