. if the average market price is between $ 18 and $ 22 on the date of the company 2019s achievement of a milestone , the relevant milestone payment will be reduced ratably . these milestone payments may be made , at the company 2019s option , with cash or stock or by a combination of cash or stock , except that no more than an aggregate of approximately $ 9.4 million of these milestone payments may be made in the form of stock