The factorial function, written as n! in math, is where you mulitply all of the whole numbers from 1 to whatever n is. Thus:

- 1! = 1 = 1
- 2! = 1 * 2 = 2
- 3! = 1 * 2 * 3 = 6
- 4! = 1 * 2 * 3 * 4 = 24
- 5! = 1 * 2 * 3 * 4 * 5 = 120
- etc...

Create an application that asks for a number from the user and displays the factorial of that number. Your program should error-check to make sure that the user hasn't entered a negative value.

- You should have:
- A Button that opens an InputBox for the number
- A Label to display the answer.

**HINTS:** Use either a Do-Loop-While or a Do-While-Loop
(you'll have to figure out which) to run not only the factorial algorithm,
but also the error-checking for numbers less than 0. Don't be afraid to add an extra variable if you need one. Use a good sentinel and a variable to keep track of the answer. Factorial numbers get really big, really fast so use a Long instead of an Integer.