#include <iostream>
#include <string>
#include <vector>
#include <queue>
#include <deque>
#include <algorithm>
#include <set>
#include <map>
#include <bitset>
#include <cmath>
#include <functional>
#include <iomanip>
#define vll vector<ll>
#define vvvl vector<vvl>
#define vvl vector<vector<ll>>
#define VV(a, b, c, d) vector<vector<d>>(a, vector<d>(b, c))
#define VVV(a, b, c, d) vector<vvl>(a, vvl(b, vll (c, d)));
#define re(c, b) for(ll c=0;c<b;c++)
#define all(obj) (obj).begin(), (obj).end()
typedef long long int ll;
typedef long double ld;
using namespace std;

bool solve(){
  string s;std::cin >> s;
  if(s.size()%2==1) return false;
  string l = s.substr(0, s.size()/2);
  string r = s.substr(s.size()/2, s.size()/2);
  //std::cout << l << " " << r << '\n';
  return l==r;
}
int main(int argc, char const *argv[]) {
  if(solve()) std::cout << "YES" << '\n';
  else std::cout << "NO" << '\n';
}