def METHOD_NAME(response_body):
    SERVICE_UNAVAILABLE_STR = 'Service Unavailable'
    HTML_HEADER_TAG_REGEX = '<h[0-9]+>(.*?)</h[0-9]+>'
    HTML_BODY_TAG_REGEX = '<BODY>(.*?)</BODY>'
    HTML_PARAGRAPH_TAG_REGEX = '<p>(.*?)</p>'
    response_body = response_body.decode() if isinstance(response_body, bytes) else response_body
    response_body = regex.compile(HTML_BODY_TAG_REGEX).findall(response_body)
    if len(response_body) >= 1:
        response_body = response_body[0]
        headers = regex.compile(HTML_HEADER_TAG_REGEX).findall(response_body)
        # explicit check of service unavailable
        if len(headers) >= 1 and headers.__contains__(SERVICE_UNAVAILABLE_STR):
            detailed_response = regex.compile(HTML_PARAGRAPH_TAG_REGEX).findall(response_body)
            resultant_response = ""
            if detailed_response is not None:
                for response in detailed_response:
                    resultant_response = resultant_response + response + "\n"
            return resultant_response
    return None