input: Write a python function to find the second smallest number in a list.
  assert second_smallest_num([45, 25, 12, 34, 36]) == 25
  assert second_smallest_num([10, 5, 8, 20, 15]) == 8
  assert second_smallest_num([3, 1, 4, 1, 5, 9, 2]) == 2
output: def second_smallest_num(lst):
      unique_lst = list(set(lst))  # Remove duplicates
      unique_lst.sort()
      if len(unique_lst) < 2:
          return None  # Not enough elements to have a second smallest
      return unique_lst[1]