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

int main() {
	string s;
	cin >> s;

	int len = s.size();
	if (len % 2 == 1) {
		cout << "NO" << endl; 
	}
	else {
		int n = len / 2;
		string a, b;
		a = s.substr(0, n);
		b = s.substr(n, n);

		if (a == b) {
			cout << "YES" << endl;
		}
		else {
			cout << "NO" << endl;
		}
	}
}