#include <iostream>
#include <string>
using namespace std;
int main(){
	string S;
	cin>>S;
	if(S.size()%2==0){
		string T;
		for(int x=0;x<S.size()/2;x++){
			T[x]=S[S.size()/2+x];
			if(T[x]!=S[x]){
				cout<<"NO"<<endl;
				return 0;
			}
		}
	}else{
		cout<<"NO"<<endl;
		return 0;
	}
	cout<<"YES"<<endl;
	return 0;
}