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