#include<iostream>
#include<string>

using namespace std;

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