//inlclude前用define 
#define _USE_MATH_DEFINES

//include
#include<iostream>
#include<string>
#include<algorithm>
#include<vector>
#include<cmath>
#include<cstdio>
#include<type_traits>
#include<numeric>
//#include<deque>
#include<limits>
#include<iomanip>
#include<set>
#include<tuple>
#include<map>

using namespace std;

//typedef
typedef vector<int> VI;
typedef vector<string> VS;
typedef vector<char> VC;
typedef long long int ll;

//define
#define INF 1000000000 
#define NUM 1000000007
#define all(x) begin(x), end(x)
#define rep(i,n) for(int i=0;i<(int)(n);i++)

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

	int size = s.size();
	if (size % 2 == 1) {
		cout << "NO" << endl;
	}
	else {
		rep(i, size / 2) {
			if (s[i] != s[i + (size / 2)]) {
				cout << "NO" << endl;
				return 0;
			}
		}

		cout << "YES" << endl;
	}
	return 0;
}