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

int main() {
	string S;
	cin >> S;
	bool same = true;
	int mid = S.size() / 2;

	if (S.size() % 2) {
		same = false;
	}
	else {
		for (int i = 0; i < mid; i++)
			if (S[i] != S[i + mid]) same = false;
	}

	cout << (same ? "YES" : "NO") << endl;

	return 0;
}