input: from typing import List
  
  def html_to_text(html_string: str) -> str:
      """ This function converts a given HTML string to plain text by removing all HTML tags.
      It iterates over each character in the HTML string, appending it to the output string 
      if it is not part of a tag.
      
      Example:
      >>> html_to_text('<p>Hello, <b>world</b>!</p>')
      'Hello, world!'
      >>> html_to_text('<a href="#">Click here</a>')
      'Click here'
      """
output:     output = ""
      in_tag = False
      
      for char in html_string:
          if char == '<':
              in_tag = True
          elif char == '>':
              in_tag = False
          elif not in_tag:
              output += char
      
      return output