#include<bits/stdc++.h>
using namespace std;
int main(){
  string s;
  cin>>s;
  int n = s.size();
  if(n%2==1){
    cout<<"NO"<<endl;
    return 0;
  }
  for(int i=0;i<n/2;i++){
    if(s[i]!=s[n/2+i]){
      cout<<"NO"<<endl;
      return 0;
    }
  }
  cout<<"YES"<<endl;
  return 0;
}