input: Write a python function that receives a list of integers and returns the second smallest number. If there is no such element, return None.
  assert second_min([1, 2, 3, 4, 5]) == 2
  assert second_min([5, 1, 4, 3, 2]) == 2
  assert second_min([]) == None
  assert second_min([1, 1]) == None
  assert second_min([1,1,1,1,0]) == 1
  assert second_min([1, 0**0]) == None
  assert second_min([-35, 34, 12, -45]) == -35
output: def second_min(lst):
      if len(lst) < 2:
          return None
      unique_lst = list(set(lst))
      if len(unique_lst) < 2:
          return None
      unique_lst.sort()
      return unique_lst[1]