#include <bits/stdc++.h>
#define rep(i,n) for(int i=0; i<(n); i++)
using namespace std;
typedef long long ll;

int main(){
	string s; cin>>s;
	int n=s.size();
	if(n%2!=0){cout << "NO" << endl; return 0;}
	rep(i,n/2){
		if(s[i]!=s[i+n/2]){
			cout << "NO" << endl;
			return 0;
		}
	}
	cout << "YES" << endl;	
}