How to auto fill blank cells in column

I need some help with Google Sheets. I have two columns, let's say A1-A100 and C1-C100. In A1-A100 I have a list of names (students), but there may be less than 100, so it could be blank from A85 to A100 for example. In C1-C100 I have grades, from 0 to 10. I need a script that auto-fills blank cells in grades (C) column with "AUS" (short for 'not present' in Spanish). But only cells corresponding to some student... so from C85 to C100, it should be left blank.

Any help would be appreciated.