#include <iostream>
#include <string>
using namespace std;
int main(){
	string S;
	cin >> S;
	int N = S.size();
	if (N % 2 == 1){
		cout << "NO" << endl;
	} else {
		if (S.substr(0, N / 2) != S.substr(N / 2)){
			cout << "NO" << endl;
		} else {
			cout << "YES" << endl;
		}
	}
}