first,I declare a variable "n" for input.
then, using while loop to set the stop line of this program
(if n equals to 1)

in the while loop,
I declare another variable "a" to decide whether n is an odd number or not,which
I determine that a is n%2.
(if a=1 then n is an odd number)

finally,using if function to decide what algorithm n should do whenever n is larger than 1.