#include <bits/stdc++.h>
#define int long long 
using namespace std;

signed main() {
string  S;
cin >> S;

int N = (int)S.size();

if( N % 2 == 1 ){
cout  << "NO" << endl;
return 0;
}

for( int i = 0; i < N/2; i++ ){
if( S.at(i) != S.at(N/2+i) ){
cout  << "NO" << endl;
return 0;
}
}

cout  << "YES" << endl;
  
}