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

int main() {
	string str; cin >> str;
	int l = str.length();
	if (l % 2 == 0) {
		for (int i = 0; i < l/2; ++i) {
			if (str[i] != str[i+l/2]) {
				cout << "NO" << endl;
				return 0;
			}
		}
		cout << "YES" << endl;
	} else cout << "NO" << endl;
	return 0;
}