#include<bits/stdc++.h>
using namespace std;
using Int = long long;
//INSERT ABOVE HERE
signed main(){
  string s;
  cin>>s;
  if(s.size()&1){
    cout<<"NO"<<endl;
    return 0;
  }
  Int x=s.size()/2;
  string a=s.substr(0,x),b=s.substr(x);
  cout<<(a==b?"YES":"NO")<<endl;
  return 0;
}