Given a positive number n, the factorial of that number, denoted
n!, is equal to 1 x 2 x ... (n - 1) x n. Assuming that n is greater
than zero and less than 12, complete the program named
`Factorial`

below, so that it computes
the value of n! for any positive n less than 12.

Input: n, the integer value for which n! is to be computed.

Output: n! -- the factorial of n