//#include<bits/stdc++.h>
#include<iostream>
#include<string>
using namespace std;

int main()
{
	string str;
	cin>>str;
	string cpstr[2];
	cpstr[0] = str.substr(0,str.length()/2);
	cpstr[1] = str.substr(str.length()/2,str.length()/2);
	if(cpstr[0] == cpstr[1])cout<<"YES"<<endl;
	else cout<<"NO"<<endl;
	return 0;
}