#include <iostream>
using namespace std;
int main() {
    string s; cin >> s;
    if (s.size() % 2 != 0) cout << "NO\n";
    else {
        for (int i = 0; i < s.size()/2; i++)
            if (s[i] != s[i+s.size()/2]) { cout << "NO\n"; return 0; }
        cout << "YES\n";
    }
}