#include<iostream>
#include<string>
using namespace std;
int main() {
	string s;
	cin >> s;
	int n = s.length();
	int k = 0;
	if (n % 2 == 1) {
		cout << "NO" << endl;
		return 0;
	}
	for (int i = 0; i < n / 2; i++) {
		if (s[i] != s[i + n / 2]) {
			k = 1;
		}
	}
	if (k == 0) {
		cout << "YES" << endl;
	}
	else {
		cout << "NO" << endl;
	}
}