input: Write a python function to find the second smallest element in an array.
  assert secondSmallest([4, 5, 6, 7, 1, 2, 4]) == 2
  assert secondSmallest([10, 20, 4, 45, 99]) == 10
  assert secondSmallest([1, 1, 1, 1]) == "No second smallest element"
output: def secondSmallest(arr):
      unique_elements = list(set(arr))
      if len(unique_elements) < 2:
          return "No second smallest element"
      unique_elements.sort()
      return unique_elements[1]