input: 
  def html_to_text(html_string: str) -> str:
      """ Convert an HTML string to a plain text string without using any libraries.
      Tags are removed, and the text between tags is preserved.
      >>> html_to_text("<p>Hello, World!</p>")
      'Hello, World!'
      >>> html_to_text("<h1>Title</h1><p>Paragraph.</p>")
      'TitleParagraph.'
      """
  
output:     import re
      text = re.sub(r'<[^>]+>', '', html_string)
      return text