#include using namespace std; using namespace std; using ll = long long; using ull = unsigned long long; using ld = long double; using P = pair; using vi = vector; using vvi = vector; #define rep(i, n) for(int i = 0; i < (n); i++) #define rep1(i, n) for(int i = 1; i <= (n); i++) #define rep2(i, x, n) for(int i = x; i < (n); i++) #define all(n) begin(n), end(n) const int INF = 1e9; const long long llINF = 1LL << 60; int dy[] = {0, 0, 1, -1}; int dx[] = {1, -1, 0, 0}; void Main() { string s; cin >> s; if(s.substr(0, s.size() / 2) == s.substr(s.size() / 2, s.size() / 2)) cout << "YES" << endl; else cout << "NO" << endl; } int main() { std::cin.tie(nullptr); std::ios_base::sync_with_stdio(false); std::cout << std::fixed << std::setprecision(15); Main(); return 0; }