#include<iostream>
#include<vector>
#include<algorithm>
#include<functional>
#include<queue>
#include<stack>
#include<set>
#include<map>
#include<unordered_map>
#include<climits>
#include<cstdlib>
#include<cmath>
#include<string>
#include<iomanip>

using namespace std;


int main() {
	string s;
	cin >> s;
	int n = s.size();
	if (n % 2) {
		cout << "NO" << endl;
		return 0;
	}
	cout << (s.substr(0, n / 2) == s.substr(n / 2, n / 2) ? "YES" : "NO") <<  endl;

	return 0;
}