#include <stdio.h>
#include <algorithm>
#include <iostream>
#include <string>
#include <vector>
#include <functional>
#include <map>
#include <iomanip>
#include <math.h> 
#include <stack>
#include <queue>
#include <bitset>
#include <cstdlib>
#include <tuple>
#include <cctype>
#include <ctype.h>
#include <set>
#include <sstream>

using namespace std;


int main() {
	int i, j, k;
	string s;

	cin >> s;

	if (s.length() % 2 != 0) {
		cout << "NO" << endl;
		return 0;
	}

	string s1, s2;

	for (i = 0; i < (s.length() / 2); i++) {
		s1 += s[i];
	}

	s.erase(0, (s.length()) / 2 );

	if (s == s1) {
		cout << "YES" << endl;
	}
	else {
		cout << "NO" << endl;
	}




	getchar();
	getchar();
	return 0;
}