500
Sisyphus and Tantulas endured this punishement in the Realm of the Dead.
What is Sisyphus was eternally struggling with pushing a boulder up a hill only to have it roll back down again whenever it reaches the top, and Tantalus was agonized by thirst and hunger- he sits in a pool of water over hung by bunches of grapes, but whenever he leans down to drink, the water sinks out of reach, and whenever he tries for the grapes, they rise out of reach?