#include <iostream>
#include <string>
using namespace std;

int main(void){
	string str;
	int i;

	cin>>str;

	size_t size=str.length();

	if(size%2!=0){
		cout<<"NO\n";
		return 0;
	}

	size/=2;

	for(i=0;i<size;i++){
		if(str[i]!=str[size+i]){
			cout<<"NO\n";
			return 0;
		}
	}

	cout<<"YES\n";
	return 0;
}