#include <iostream>
#include <string>
#include <string.h>
using namespace std;
int main(int argc, char* argv[])
{
	string S;
	cin>>S;
	size_t sLen=S.length();
	if (sLen%2==1){
		cout<<"NO"<<endl;
		return 0;
	}
	char *p=(char*)S.c_str();
	if (!memcmp(p,p+sLen/2,sLen/2)){
		cout<<"YES"<<endl;
	}else{
		cout<<"NO"<<endl;
	}
	return 0;
}