#include<bits/stdc++.h>
#define rep(i, x) for(ll i = 0; i < x; i++)
#define rep2(i, x) for(ll i = 1; i <= x; i++)
#define all(a) (a).begin(),(a).end()
using ll = long long;
using ld = long double;
using namespace std;
signed main() {
    string s; cin >> s; ll n = s.size();
	if (n % 2 == 1) { cout << "NO\n"; return 0; }
	rep(i, n / 2) {
		if (s[i] != s[i + n / 2]) { cout << "NO\n"; return 0; }
	}
	cout << "YES\n";
	return 0;
}