Aluminum foil has a thickness of 0.025mm. A roll is formed by tightly winding it around a tube with an outside diameter of 4cm. Given the length of the foil in cm, write a function that returns the diameter of the roll in cm measured at its THICKEST point. Round the result to four places.
foil(0) ➞ 4.0
foil(50) ➞ 4.02
foil(4321) ➞ 5.4575
foil(10000) ➞ 6.9175N/A