#include <bits/stdc++.h>

using namespace std;

typedef unsigned long long ull;
typedef long long ll;

int main(){
	string s;
	cin >> s;
	if(s.length()%2!=0){
		cout << "NO" << endl;
	}else{
		int n=s.length();
		if(s.substr(0, n/2)!=s.substr(n/2, n/2)){
			cout << "NO" << endl;
		}else cout << "YES" << endl;
	}
	return 0;
}