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

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