I have a database of containers, example as follows:

Column A Column B Column C Column D
Port Load Port Unload Cntr Size Container No
ANT MTL 20 AA123456
ANT MTL 20 AA123456
ANT MTL 20 BC109876
HAM LEH 40 DD294567

I have a formula which counts the number of containers
={COUNT(IF(A1:A100="ANT",IF(B1:B100="MTL",IF(C1:C1 00=20,D1:D100))))}
when entered as an array counts the containers I want, but my problem is that
I want to exclude duplicated containers in column D.

Any suggestions as to how I could achieve this?

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