input: def html_to_text(html_string: str) -> str:
      """Convert a given 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>This is a <a href="#">link</a>.</div>')
      'This is a link.'
      """
output:     import re
      return re.sub(r'<[^>]+>', '', html_string)