input: from typing import List
  
  def html_to_text(html_string: str) -> str:
      """
      Convert HTML to plain text without using any libraries.
      The function should ignore all HTML tags and only extract the text content from the HTML string.
      
      >>> html_to_text('<p>Hello, <b>world</b>!</p>')
      'Hello, world!'
      >>> html_to_text('<a href="example.com">This is a link</a>')
      'This is a link'
      >>> html_to_text('<div><p>Paragraph 1</p><p>Paragraph 2</p></div>')
      'Paragraph 1Paragraph 2'
      """
output:     text = ''
      inside_tag = False
      for char in html_string:
          if char == '<':
              inside_tag = True
          elif char == '>':
              inside_tag = False
          elif not inside_tag:
              text += char
      return text