Factorial By Countdown

Write def factorial(n: int) -> int that returns n factorial, the product of every whole number from 1 up to n, using a while loop that counts down from n and multiplies a running result each pass; no recursion and no imports. The factorial of 0 is 1. Do NOT write a main block or any top-level test code; the tests construct the calls. Input: one line, a whole number of 0 or more, which the tests read and pass to your function before printing the value it returns.