def f(l,xs)
	ans=0
	xs.each{|x|
		ans+=(x/l).to_i
	}
	return ans
end
def fb(l,r,k,xs,d)
	if d>77then
		return l
	else
		m=(l+r)/2.0
		k2=f(m,xs)
		if k2<k then
			return fb(l,m,k,xs,d+1)
		else
			return fb(m,r,k,xs,d+1)
		end
	end
end
n=gets.to_i
xs=gets.split(" ").map{|e| e.to_f}
k=gets.to_i
puts sprintf("%0.11f",fb(0.0,xs.max,k,xs,0))