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


int main() {
	string s;
	cin >> s;

	int n = (int)s.length();
	if (n % 2 != 0) {
		cout << "NO" << endl;
		return 0;
	}
	bool flag=true;
	for (int i = 0; i < n / 2; i++) {
		if (s[i] != s[n / 2 + i]) {
			flag = false;
			break;
		}
	}

	cout << (flag?"YES":"NO") << endl;
}