#include<iostream>
#include<cstring>

using namespace std;

int main(void){
	int  x;
	char str[20];
	cin >> str;
	x = strlen(str);
	if(x%2==1){cout << "NO\n";return 0;}
	x = x/2;
	for(int i=0;i<x;i++){
	 if(str[i]!=str[x+i]){cout << "NO\n";return 0;}
	}
	cout << "YES\n";
	return 0;
}