#include <bits/stdc++.h>
using namespace std;

int main() {
  string s;
  cin >> s;
  auto n = s.size();
  string t = s.substr(0, n / 2);
  string u = s.substr(n / 2, n - n / 2);
  cout << (t == u ? "YES" : "NO") << endl;
  return 0;
}