#include <iostream>
#include <string>
#include <math.h>
using namespace std;
int main() {
	string S;
	cin >> S;
	double d = (double)S.size()/2;
	int size = (int)(ceil(d));
	string Ss = S.substr(size,size);
	S.erase(S.begin() + size,S.end());
	if (S == Ss) {
		cout << "YES" << endl;
	}
	else if (S != Ss) {
		cout << "NO" << endl;;
	}
	return 0;
}