import java.util.Scanner;

public class No739
{
	public static void main(String args[])
	{
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		int l = s.length();

		String ans = "";
		String h = s.substring( 0, l/2 );
		String r = s.substring( l/2, l );

// 文字列の比較にはequalsメソッドを使う
		if( h.equals(r) ){ ans = "YES"; }
		else{ ans = "NO"; }

		System.out.println( ans );
	}
}