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