just a word of caution for anyone thinking of buying a ticket from a secondary site. often these sites will take your payment without the guarantee of an actual ticket, and then attempt to buy a ticket for you.
If they fail, they just refund your number (eventually). So only buy from one of the big, well known players in the market (Viagogo, stubhub etc) or try to do full research on the company offering you a ticket, and make sure they tell you the seat number they are selling.