#[macro_export]
macro_rules! setup {
    { mut $input:ident: SplitWhitespace $(,)? } => {
        use std::io::Read;
        let mut buf = String::new();
        std::io::stdin().read_to_string(&mut buf).ok();
        let mut $input = buf.split_whitespace();
    };
}

#[macro_export]
macro_rules! parse_next {
    ($str_iter:expr) => {
        $str_iter.next().unwrap().parse().ok().unwrap()
    };
}

fn main() {
    setup! { mut input: SplitWhitespace };

    let s: String = parse_next!(input);

    let len = s.chars().count();

    if len % 2 != 0 {
        println!("NO");
        return;
    }

    let ans = match (|| {
        let first = s.chars().take(len / 2).collect::<String>();
        let last = s.chars().skip(len / 2).collect::<String>();
        return first == last;
    })() {
        true => "YES",
        false => "NO",
    };

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