input: def third_largest(lst):
      """Given a list of numbers, return the third largest element in the list.
      If there are fewer than three elements in the list, return None.
      >>> third_largest([12, 13, 13, 45, 22, 99])
      22
      >>> third_largest([5, 3, 8, 2, 9, 1])
      5
      """
output:     if len(lst) < 3:
          return None
      sorted_lst = sorted(set(lst), reverse=True)
      return sorted_lst[2]