i think countif formula but not sure..

I have this sheet here with 40 locations which are the same but are over 3 different warehouses, where there is a location full in one warehouse there is one empty in another, and also there is locations occupied in all 3 warehouses..i am trying to write a formula which out of the 40 total locations over the 3 warehouses will give me the number of locations empty without counting duplicates as all 3 warehouses and locations exist under the one building..there is "yes, no" against locations throughout the sheet against the different warehouses indicating if there occupied or not..i have tried and researched this but have had no success so far...

Credit to adhawan06 who helped me with first part of this spreadsheet