#include <fstream>
#include <iostream>
#include <string>


int main() {

	//std::ifstream inf("Text.txt");	std::cin.rdbuf(inf.rdbuf());
	std::string S;
	std::cin >> S;

	if (S.length() % 2 == 0) {
		if (S.substr(0, S.length() / 2) == S.substr(S.length() / 2, S.length() / 2)) {
			std::cout << "YES" << std::endl;
			return 0;
		}
	}

	std::cout << "NO" << std::endl;

	return 0;
}