#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
#include <queue>
#include <cmath>
#include <map>

int main(void) {

	std::string s;

	std::cin >> s;

	std::string t = s.substr(0, s.length() / 2);

	if (s == t + t) {
		std::cout << "YES" << std::endl;
	}
	else {
		std::cout << "NO" << std::endl;
	}

	return 0;
}