Hi, if there are any conditional formatting wizards out there, please help............

This relates to Excel 2013.

On a marksheet:
  • D1 to K1 are exam question marks (8 exam questions, students will answer 4).
  • L1 is the Overall exam total, '=SUM(D1:K1)/4'
I would like L1 to fill red if only 3 values have been entered into cells D1 to K1. The marking scale is 0 to 100.
This red conditional formatting will indicate that an exam question mark may be is missing, and the exam script needs to be checked.
Any ideas?

Many thanks!