#include <iostream>
#define REP(i, I, n) for (int i = I; i < n; i++)
using namespace std;

int main() {
    string s;
    cin >> s;
    if (s.size() % 2 != 0) {
        cout << "NO" << endl;
        return 0;
    }
    string s1, s2;
    REP(i, 0, s.size() / 2) {
        s1 += s[i];
    }
    REP(i, s.size() / 2, s.size()) {
        s2 += s[i];
    }
    if (s1 == s2) cout << "YES";
    else cout << "NO";
    cout << endl;
    return 0;
}