let () = 
	let make_row n =
		let buf = Buffer.create n in
		for i = 1 to n + 1 do 
			Buffer.add_char buf (if i mod 2 = 1 then '#' else '.');
		done;
		let str = Buffer.contents buf in
		(Str.string_before str n, Str.string_after str 1) in
		
    let rec f _ = 
        let (h, w) = Scanf.sscanf(read_line()) "%d %d" (fun x y -> (x, y)) in
        if h = 0 && w = 0 then ()
        else (
            let (odd_row, even_row) = make_row w in
            for i = 1 to h do
            	Printf.printf "%s\n" (if i mod 2 = 1 then odd_row else even_row);
            done;
            print_newline ();
            f ()
        )
        
    in f ();;
