Multiple if isna

If the contents of both AF2 and AH2 = #N/A Then AK2 0
That covers where boths columns have #N/A
If the contents of AF2 = #N/A Then AK2 = AH2
That covers where just column AF has #N/A
If the contents of AH2 = #N/A Then AK2 = AF2
That covers where just column AH has #N/A

Formula:

=IF(AND(ISNA(AF2),ISNA(AH2)),0,IF(ISNA(AF2),AH2,IF(ISNA(AH2),AF2,"what now?")))

Regards, TMS