#include <algorithm>
#include <iostream>
#include <string>
#include <vector>
using namespace std;
int main(void) {
  string S;
  cin >> S;
  if((int)S.size() % 2 != 0) {
    cout << "NO" << endl;
    return 0;
  }
  int n = S.size() / 2;
  for(int i = 0; i < n; i++) {
    if(S[i] != S[i + n]) {
      cout << "NO" << endl;
      return 0;
    }
  }
  cout << "YES" << endl;
  return 0;
}