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

int main() {
string s;
cin >> s;
int n = s.size();

if (n % 2 == 1) {
  cout << "NO" << endl;
  return 0;
}

string s1, s2;
s1 = (0, n/2);
s2 = (n/2, n/2);

if (s1 == s2) {
  cout << "YES" << endl;
} else {
  cout << "NO" << endl;
}
return 0;
}