#include <bits/stdc++.h>

using namespace std;

int main() {
    string s;
    int word_len;
    
    cin >> s;
    
    if (s.length() % 2 != 0) {
        cout << "NO" << endl;
        return 0;
    }
    
    word_len = s.length() / 2;
    if (s.substr(0, word_len) == s.substr(s.length() - word_len, word_len)) {
        cout << "YES" << endl;
    } else {
        cout << "NO" << endl;
    }
    
    return 0;
}