#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
  #define _GLIBCXX_DEBUG
#else
  #define Debug(...) void(0)
#endif
using ll = long long;
#define rep(i, n) for (int i = 0; i < (n); ++i)

int main() {
  string s;
  cin >> s;
  if (s.size() % 2 == 1) {
    cout << "NO" << endl;
  }
  else {
    string t = s.substr(0, s.size() / 2);
    if (t + t == s) {
      cout << "YES" << endl;
    }
    else {
      cout << "NO" << endl;
    }
  }
  return 0;
}