#include <bits/stdc++.h>

using namespace std;

int main() {
	string s;
	cin >> s;
	int l = s.length();
	if (l % 2 == 0 && s.substr(0, l / 2) == s.substr(l / 2, l / 2)) {
		cout << "YES" << endl;
	} else {
		cout << "NO" << endl;
	}
	return 0;
}