Write a program that tells a missing side of a right-angled triangle. It asks the user which side of the triangle is missing (in a string). It then finds that missing side using the famous Pythagoras theorem. Use the required built-in functions.

Note: You can ask user to enter any of these three inputs (perpendicular, base, hypotenuse). If the user enters wrong spelling i.e. any string other than above three, display WRONG Input on screen and ask input again. You can use an infinite loop for asking input again and again.