You would have had to purchase them at the airport, where they cost $5 more each. Or you would have been relegated back to Y, if seats were available.
[Edited to add:] They cost $5 more only if you purchase them from an agent. You can purchase them at a kiosk with no premium.
Last edited by vasantn; Feb 18, 2008 at 8:31 pm
Reason: correction of error pointed out by miamigrad