If the condo has 23 floors and the top 2 floors are reserved for penthouse then there are 23-2 = <<23-2=21>>21 floors for regular units
If a regular floor has 12 units each, then 21 regular floors would have 12*21 = <<12*21=252>>252 units
If a penthouse floor has 2 units each, then 2 penthouse floors would have 2*2 = <<2*2=4>>4 units
The total units in the property would then be 252 regular + 4 penthouse or 252+4 = <<252+4=256>>256 units
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