#include using namespace std; int main() { string s; cin >> s; int n = s.size(); if (n % 2 == 1) { cout << "NO" << endl; return 0; } string s1, s2; s1 = (0, n/2); s2 = (n/2, n/2); if (s1 == s2) { cout << "YES" << endl; } else { cout << "NO" << endl; } return 0; }