#include <iostream>
#include <string>
using namespace std;
int main(void) {
	string s;
	cin >> s;
	int n = s.size();
	string ans = "NO";
	if (n % 2 == 0) {
		if (s.substr(0, n / 2) == s.substr(n / 2))
			ans = "YES";
	}
	cout << ans << endl;
	return 0;
}