#include<iostream>
#include<string>
#include<vector>
#include<algorithm>
#include<map>
#define all(x) x.begin(),x.end()
#define pb push_back
#define ll long long 
#define P pair<int,int>
#define LP pair<ll,ll>
using namespace std;
int main() {
	string s;
	cin >> s;
	bool f = 0;
	if (s.length() %2==0) {
		if(s.substr(0,s.length()/2)==s.substr(s.length()/2)) f=1;
	}

	if (f) cout << "YES" << endl;
	else cout << "NO" << endl;
	return 0;
}