input: Write a function to extract domain name from a given URL using regular expressions.
  assert extract_domain_name("https://www.example.com/path") == "example.com"
  assert extract_domain_name("http://subdomain.example.org") == "example.org"
  assert extract_domain_name("https://example.net/about") == "example.net"
output: def extract_domain_name(url):
      import re
      pattern = r"https?://(?:www\.)?([^/]+)"
      match = re.search(pattern, url)
      if match:
          domain = match.group(1)
          return '.'.join(domain.split('.')[-2:])
      return None