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

int main() {
	string S;
	cin >> S;
	if (S.size() % 2 == 1) cout << "NO" << endl;
	else {
		if (S.substr(0, S.size() / 2) == S.substr(S.size() / 2, S.size() / 2)) cout << "YES" << endl;
		else cout << "NO" << endl;
	}
}