input: Write a function to convert HTML to plain text without using any libraries. If the input HTML string is empty, return an empty string.
  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('<html><body><h1>Title</h1>Some text</body></html>')=='TitleSome text'
  assert html_to_text('<a href="#">Link</a>')=='Link'
  assert html_to_text('<p>Paragraph with <b>bold</b> text</p>')=='Paragraph with bold text'
  assert html_to_text('')==''
  assert html_to_text('<br>')==''
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