input: Write a python function to calculate the cost of a pizza based on its size.
  assert pizzaCost(14) == 10.00
  assert pizzaCost(16) == 12.50
  assert pizzaCost(18) == 15.00
  assert pizzaCost(20) == "Unknown size"
output: def pizzaCost(size):
      if size == 14:
          return 10.00
      elif size == 16:
          return 12.50
      elif size == 18:
          return 15.00
      else:
          return "Unknown size"