numbers in thousand and million

Hello everyone,
I am trying to save space by shorting my numbers.
i gave an example in the file below, i know how to manually set-up each cell in either thousands or millions. but since my sheet has data validation in column K, the number in column will vary depending on the data of K, so i would like to have the column M to automatically write the number in single digit,thousands or millions if possible.

thank you