input: Write a function to convert a given HTML string to plain text without using any libraries. If the given HTML string is empty then 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("<p>Hello, <b>world</b>!</p>")=="Hello, world!"
  assert html_to_text("<h1>Title</h1>")=="Title"
  assert html_to_text("<ul><li>item1</li><li>item2</li></ul>")=="item1item2"
  assert html_to_text("")==""
  assert html_to_text("<div>Some text</div>")=="Some text"
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