func main()
	var n: int :: cui@inputInt()
	
	var x: float :: 1000.0
	for(1, n - 1)
		var a: int :: cui@inputInt()
		do x :* (1000 - a) $ float / 1000.0
	end for
	
	var ans: float :: 1000.0 - x
	do cui@print("\{ans}\n")
end func