Dancers of the state opera ballet perform during a dress rehearsal for the Opera Ball in Vienna February 11, 2015. The traditional ball is opened by the Austrian president and features a musical programme with solists and artists from the Vienna Philharmonic and State Ballet before the 144 debutants and debutantes lead into the festivities with a Strauss waltz. Tickets start at 250 euros ($340) and a box costs as much as 18,500 euros ($25,000). REUTERS/Leonhard Foeger (AUSTRIA - Tags: ENTERTAINMENT SOCIETY)