input: def third_largest(lst):
      """
      Get the third largest element in a given list.
      >>> third_largest([12, 13, 13, 45, 22, 99])
      22
      """
output:     if len(lst) < 3:
          return None
      sorted_lst = sorted(set(lst), reverse=True)
      if len(sorted_lst) < 3:
          return None
      return sorted_lst[2]