Using IF formula for Student Grades

This is my IF formula for grading students:

=IF(G16>=627,"C1",IF(G16>=543,"B2",IF(G16>=460,"B1",IF(G16>=337,"A2","N/A"))))

I want a "N/A" result if the student doesn't have a score. At he moment I have students with "N/A" (no score) in column G who get a C1 with the above formula. Thanks!

Yes, that works, Glenn, though I changed "" to "N/A" like this:

=IF(G16="N/A","N/A",IF(G16>=627,"C1",IF(G16>=543,"B2",IF(G16>=460,"B1",IF(G16>=337,"A2","N/A")))))

But I couldn't have done that without you. Thanks very much!