#include <bits/stdc++.h>

using namespace std;

int main() {
  string s;
  cin >> s;
  int n = s.size();
  if (n % 2 != 0) {
    puts("NO");
    return 0;
  }

  bool good = true;
  for (int i = 0, j = n / 2; i < n / 2; ++i, ++j) {
    if (s[i] != s[j]) good = false;
  }
  if (good) puts("YES");
  else puts("NO");
}