Mill and the utilitarian doctrine

According to Mill and the utilitarian doctrine, happiness is the
purpose of human existence. How would Kant argue against this claim?
Prompt 1.
Sources allow :

  • Mill's Utilitarianism
  • Grounding for the Metaphysics of Morals: with On a Supposed Right to Lie because of Philanthropic
    Concerns (Hackett Classics) 3rd Edition