New to Gosu, Help

hello, I am new to ruby and am learning to make an image in gosu
this code is meant to open the window, but it says there is an error (unepected end of input, expecting end)
the code is as follows

require 'rubygems'
require 'gosu'

# we will draw on the demowindow on screen
class DemoWindow< Gosu::Window #the class is used to define the window
  def initialize
    super (640, 400, false) # (width, height, fullscreen?)
end #this make the application open

can someone help,

ps: i am using this tutorial to learn the very basics for gosu

I think there should be no space between super and (...):

super(640, 400, false) # (width, height, fullscreen?)