fn main() {
	let mut s = String::new();
	std::io::stdin().read_line(&mut s).ok();
	let s = s.trim();
	let s2 = &s[..s.len() / 2];
	
	if s.to_string() == s2.repeat(2) {
		println!("YES");
	} else {
		println!("NO");
	}
}