#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cstdlib>
#include<vector>
#include<string>
#include<sstream>
#include<cmath>
#include<numeric>
#include<map>
#include<stack>
#include<queue>
using namespace std;


int main(void) {
  string s; cin >> s;
  int n = s.size();
  if(s.size()%2==1) cout << "NO" << endl;
  else {
    for(int i=0; i<n/2; i++) {
      if(s[i] != s[i+n/2]) {
        cout << "NO" << endl;
        return 0;
      }
    }
    cout << "YES" << endl;
  }
  return 0;
}






// EOF