Countdown (Counting down from n)

There is a countdown before rockets liftoff into space–you can see an example in this YouTube video: https://www.youtube.com/watch?v=Vfn_u768UoQ

Write a program countdown.py that has the user enter a value n that the countdown will begin at. The program should then print the numbers from n down to and including 0 before printing “Blastoff!”