fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
  }

fn main() {
    let s: String = read();

    let ans = if s.len() % 2 != 0 {
        "NO"
    } else if &s[0..(s.len() / 2)] != &s[(s.len() / 2)..(s.len())] {
        "NO"
    } else {
        "YES"
    };

    println!("{}", ans);
}