The ethical system that defines acceptable behavior as that which maximizes benefits for the individual is called "Egoism." Egoism is an ethical theory that treats self-interest as the foundation of morality, stating that actions are morally right if they maximize benefits for the individual acting.

In contrast, utilitarianism is an ethical system that defines acceptable behavior as that which maximizes overall benefits or happiness for the greatest number of people, not just the individual.

Thus, the correct ethical system focused on the individual's benefit is Egoism.