#define _USE_MATH_DEFINES
#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<string>
#include<iostream>
#include<iostream>
#include<cctype>
#include<cstdio>
#include<vector>
#include<stack>
#include<queue>
#include <algorithm>
#include<math.h>
#include<set>
#include<map>
#include <sstream>
#include<iomanip>
#include <ctype.h>
using namespace std;

//#include<bits/stdc++.h>


int main() {

	string p;
	cin >> p;

	string a = p.substr(0, p.size() / 2);
	string b = p.substr(p.size()/2 , p.size() -1);

	//cout << a<<" " << b;

	if (a == b&&p.size()%2==0)cout << "YES" << endl;
	else cout << "NO" << endl;
	


	return 0;
}