Read in 'marks.txt'. The file format is one number per line. Your program will run through all these numbers, and ensure that they are valid input.

Create two lists: one for valid numbers, one for invalid numbers.

For a number to be valid, the number:

Must not have any letters inside of it

Must be greater than or equal to 0

Must be less than or equal to 100

Print out the list of bad inputs, and print out the average of the good inputs.