use std::io::Read;

fn solve(s: &str) {
    let half: usize = s.len() / 2;
    if s.len() % 2 == 1 || s[..half] != s[half..] {
        println!("{}", "NO");
    } else {
        println!("{}", "YES");
    }
}

fn main() {
    let mut s = String::new();
    std::io::stdin().read_to_string(&mut s).ok();
    let s: &str = s.trim().split('\n').next().unwrap().trim();
    solve(s);
}