There are 20 - 2 = <<20-2=18>>18 floors that are each 3 meters high.
So the first 18 floors is 18 x 3 = <<18*3=54>>54 meters high.
The last two floors are each 3 + 0.5 = <<3+0.5=3.5>>3.5 meters high.
So the total height of the last two floors is 3.5 x 2 = <<3.5*2=7>>7 meters.
Therefore, the building is 54 + 7 = <<54+7=61>>61 meters high.
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