What to enter in cell A7 to EXCLUDE anything that appears in cells A3-A6 linked to SUMIFS

The title perhaps does not explain this well.
I have a table of info whch has come from 3 criteria SUMIFS.
The SUMIFS links to text typed in column A - first row is A3, next A4 etc etc - this is all working fine! (although it may be a little untidy)
on the bottom row col A, I want to type text to Exclude the text categories already in A3,AA4,A5,etc
When I use <> before the first set to exclue it works, but won't work for multiples i.e. <>a,<>d,<>g

I have attached a copy which will hopefully make more sense
I have to detail some individually and on the others I just want the sum of anything except, as the details & number of exceptions could change

Any help would be appreciated