#include <algorithm>
#include <cmath>
#include <cstdio>
#include <deque>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>

using namespace std;

typedef long long ll;

#define MOD 1000000007

int main() {
  string s;
  cin >> s;
  int n = s.size();
  if (n & 1) {
    cout << "NO" << endl;
    return 0;
  }
  string s1 = s.substr(0, n / 2);
  string s2 = s.substr(n / 2, n / 2);
  cout << (s1 == s2 ? "YES" : "NO") << endl;
  return 0;
}