A supply chain manager uses the EOQ method with variable supply costs. The standard price is c1, but a discounted price c2 is available if the order quantity exceeds a threshold h. The manager calculates the optimal standard EOQ (Q) and finds it is 500 units. The supplier's threshold h is 600 units. The manager then calculates the intersection point a (where total costs at standard and discounted prices are equal, y1(Q) = y2(a)) and finds a = 700 units. What is the strictly optimal order quantity to minimize total costs?