Old MacDonald decided to order a special feed container which can hold the new feed that he orders for his animals. But the container store can only sell him sizes of feed containers in units of $200$lbs of capacity. $($That is$,$ they sell $200$lb capacity, $400$lb capacity, $600$lb capacity, and so on$.)$ What is the smallest size Old MacDonald needs to order so that it is large enough to hold his optimal order quantity?