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

int main()
{
    string s;
    cin >> s;

    int n = s.size();
    if (n % 2) return cout << "NO" << endl, 0;
    cout << (s.substr(0, n / 2) == s.substr(n / 2, n / 2) ? "YES" : "NO") <<  endl;

    return 0;
}