#include <bits/stdc++.h>
using namespace std;

int main() {
    string s;
    cin>>s;
    if(s.size()&1){
        cout << "NO" << endl;
        return 0;
    }
    if(s.substr(0,s.size()/2)==s.substr(s.size()/2,s.size()/2)){
        cout << "YES" << endl;
    }else cout << "NO" << endl;
    return 0;
}