Midterm exam

Midterm Exam I have one short answer question on the midterm.
I tell the students if they know the answer and can get it they will get 4 points. However if they do not know the answer they have two options:

1. Try to B**S** and get Zero
2. Write I don't know and get one point for honesty

I wonder what the results will be? And if I could I would like to have a punitive point for B#**S**. I have to check with the Dean first!