// includes {{{
#include<iostream>
#include<iomanip>
#include<algorithm>
#include<vector>
#include<stack>
#include<queue>
#include<deque>
#include<map>
#include<set>
#include<tuple>
#include<cmath>
#include<random>
#include<cassert>
// }}}
// #include<bits/stdc++.h>
using namespace std;
using ll = long long;

int main() {
  std::ios::sync_with_stdio(false), std::cin.tie(0);
  string s; cin >> s;
  int n = s.size();
#define POS(x) cout<<((x)?"POSSIBLE":"IMPOSSIBLE")<<endl;
#define Pos(x) cout<<((x)?"Possible":"Impossible")<<endl;
#define YES(x) cout<<((x)?"YES":"NO")<<endl;
#define Yes(x) cout<<((x)?"Yes":"No")<<endl;
#define yes(x) cout<<((x)?"yes":"no")<<endl;
  
  YES(n%2 == 0 && (s.substr(n/2, n/2) == s.substr(0, n/2)));
  return 0;
}