input: Write a function to convert HTML to plain text without using any libraries. The function should handle stripping out HTML tags and return the plain text.
  def html_to_text(html_string):
      output = ''
      in_tag = False
      for char in html_string:
          if char == '<':
              in_tag = True
          elif char == '>':
              in_tag = False
          elif in_tag == False:
              output += char
      return output
  
  assert html_to_text("<p>Hello, <strong>world</strong>!</p>")=='Hello, world!'
output: def html_to_text(html_string):
      output = ''
      in_tag = False
      for char in html_string:
          if char == '<':
              in_tag = True
          elif char == '>':
              in_tag = False
          elif in_tag == False:
              output += char
      return output