I'd hate to advise anyone to buy during such a spectacular run-up. However, I saw it run to 28 dollars the last time and went ahead and bought 100 shares at 25 dollars. When it fell to between 17 and 18, I bought 500 more and I was still glad I did, even when it fell to the 12s.
Anyhow, I guess you could decide how many shares you would like and then buy 10% of that now and another 10% if it pulls back a bit. You could get lucky and see it pull back to 18 or 20 but I wouldn't count on it.