#include <bits/stdc++.h>
using namespace std;
int main(){
    string s; cin >> s;
    int n = s.size();
    if(n % 2) cout << "NO" << endl;
    else if(s.substr(0, n / 2) == s.substr(n / 2, n / 2)) cout << "YES" << endl;
    else cout << "NO" << endl;
}