C# lang.

Question

 The factorial of a nonnegative integer n is written n! (pronounced "n factorial") and is defined as follows: n! = n · (n - 1) · (n - 2) · ... · 1   (for values of n greater than or equal to 1) and n! = 1   (for n = 0). For example, 5! = 5 · 4 · 3 · 2 · 1, which is 120. 

Write an application that reads a nonnegative integer from an input dialog and computes and prints its factorial.