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

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);
	string s;cin >> s;
	int n=s.size()/2;
	if(s.size()%2==1) cout << "NO" << endl;
	else{
		if(s.substr(0,n)==s.substr(n,n)) cout << "YES" << endl;
		else cout << "NO" << endl;
	}
}