How Many Bidders to Recruit

Each bidder Esubi recruits costs 4 dollars and places an independent bid Uniform(200, 1800). The item sells at the 4th highest bid, so she needs at least 4 bidders. For $n$ independent bids uniform on $(a,b)$, the expected $i$th highest bid is $a + (b-a),\frac{n + 1 - i}{n + 1}.$

How many bidders maximise her expected profit, meaning sale price minus total recruiting cost?

Answer format: enter an integer.