I have this formula that looks for a match on another worksheet:

=IF(ISNA(MATCH(F8,NSN6!A:A,0)),"N/A",INDEX(NSN6!D:D,MATCH(F8,NSN6!A:A,0)))

I need this scenario added to the formula: First look at NSN6 for match.
If found, input match. If no match found, look on NSN5 for match. If found,
input match. If not found on either worksheet, input N/A.