input: 
  def html_to_text(html_string: str) -> str:
      """
      Convert an HTML string to plain text by removing all HTML tags.
      >>> html_to_text('<p>Hello, <b>World</b>!</p>')
      'Hello, World!'
      >>> html_to_text('<div><h1>Title</h1><p>This is a paragraph.</p></div>')
      'TitleThis is a paragraph.'
      """
  
output:     import re
      return re.sub(r'<[^>]+>', '', html_string)