#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();
	if(n%2==0 && s.substr(0,n/2)==s.substr(n/2,n/2)) cout << "YES" << endl;
	else cout << "NO" << endl;
}