#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;
using ll = long long;

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

    size_t n = s.size();
    string t0 = s.substr(0, n / 2);
    string t1 = s.substr(n / 2);

    cout << ((n % 2 == 0 && t0 == t1) ? "YES" : "NO") << endl;

    return 0;
}