Janessa starts with 4 cards + 13 cards = <<4+13=17>>17 cards.
She adds 17 cards + 36 cards = <<17+36=53>>53 cards from the eBay purchase.
Janessa decides to throw away 53 cards - 4 cards = <<53-4=49>>49 cards due to damage.
After giving Dexter the present we know that Janessa kept 49 cards - 29 cards = <<49-29=20>>20 cards for herself.
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