#include <iostream>
#include <string>
using namespace std;

string s;

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