Suppose you are deciding how many donuts to eat for breakfast. The first donut gives you $4 worth of enjoyment, the second donut gives you $3 worth of enjoyment, the third $2 worth of enjoyment, the fourth $1 worth of enjoyment, and any additional donuts give you $0 worth of enjoyment, or no marginal benefit. If it costs $2.50 to purchase a donut, what is the optimal number of donuts to buy?