#include <bits/stdc++.h>
using namespace std;

int main()
{
	string S;
	cin >> S;

	int N = S.size();
	string ans = "YES";
	if( N % 2 ) ans = "NO";
	else if( S.substr( 0, N / 2 ) != S.substr( N / 2, N / 2 ) ) ans = "NO";

	cout << ans << endl;
}