use std::io::stdin;

fn main() {
    let mut buf = String::new();
    stdin().read_line(&mut buf).unwrap();
    let buf = buf.trim().to_string();
    let chars = buf.as_bytes();
    let n = chars.len();
    if n % 2 != 0 {
        println!("NO");
        return;
    }
    
    let front = &chars[0..n/2];
    let behind = &chars[n/2..n];
    if front == behind {
        println!("YES");
    } else {
        println!("NO");
    }
    
}