#include <bits/stdc++.h>
using namespace std;
using lint = long long int;
template<class T = int> using V = vector<T>;
template<class T = int> using VV = V< V<T> >;
template<class T> void assign(V<T>& v, int n, const T& a = T()) { v.assign(n, a); }
template<class T, class... U> void assign(V<T>& v, int n, const U&... u) { v.resize(n); for (auto&& i : v) assign(i, u...); }

int main() {
  cin.tie(NULL); ios::sync_with_stdio(false);
  string s; cin >> s;
  int n = s.size();
  if (n & 1) return cout << "NO" << '\n', 0;
  cout << (s.substr(0, n / 2) == s.substr(n / 2, n / 2) ? "YES" : "NO") << '\n';
}