#include <bits/stdc++.h>
#define rep(i, ss, ee) for (int i = ss; i < ee; ++i)
using namespace std;

void solve() {
  string s;
  cin >> s;
  size_t x = s.size() / 2;
  cout << ((s.substr(0, x) == (s.substr(x))) ? "YES" : "NO") << endl;
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  solve();
  getchar();
}