input: Write a python function to find the third smallest element in a list.
  assert thirdSmallest([5, 3, 8, 4, 2, 9, 1, 7]) == 3
  assert thirdSmallest([10, 20, 30, 40, 50]) == 30
  assert thirdSmallest([12, 15, 10, 11, 14, 13]) == 12
output: def thirdSmallest(arr):
      if len(arr) < 3:
          raise ValueError("List must contain at least three elements")
      arr = sorted(arr)
      return arr[2]