input: 
  def html_to_text(html_string: str) -> str:
      """ Convert HTML string to plain text without using any libraries.
      Ignores any text inside HTML tags.
      >>> html_to_text('<p>Hello, <b>world</b>!</p>')
      'Hello, world!'
      >>> html_to_text('<h1>Title</h1><p>This is a paragraph.</p>')
      'TitleThis is a paragraph.'
      """
  
output:     
      result = []
      inside_tag = False
      
      for char in html_string:
          if char == '<':
              inside_tag = True
          elif char == '>':
              inside_tag = False
          elif not inside_tag:
              result.append(char)
      
      return ''.join(result)
  