Revellers relax inside a 3-D Luminarium inflatable installation by British designer Alan Parkinson during Sziget music festival on an island in the Danube River in Budapest, Hungary August 12, 2015. (Photo by Laszlo Balogh/Reuters)

Revellers play with foam during the Sziget music festival on an island in the Danube River in Budapest, Hungary August 12, 2015. (Photo by Laszlo Balogh/Reuters)

Revellers relax inside a 3-D Luminarium inflatable installation by British designer Alan Parkinson during Sziget music festival on an island in the Danube River in Budapest, Hungary August 12, 2015. (Photo by Laszlo Balogh/Reuters)

Revellers play with foam during the Sziget music festival on an island in the Danube River in Budapest, Hungary August 12, 2015. (Photo by Laszlo Balogh/Reuters)

Revellers relax inside a 3-D Luminarium inflatable installation by British designer Alan Parkinson during Sziget music festival on an island in the Danube River in Budapest, Hungary August 12, 2015. (Photo by Laszlo Balogh/Reuters)

Reveller relax inside a 3-D Luminarium inflatable installation by British designer Alan Parkinson during Sziget music festival on an island in the Danube River in Budapest, Hungary August 12, 2015. (Photo by Laszlo Balogh/Reuters)

Revellers relax inside a 3-D Luminarium inflatable installation by British designer Alan Parkinson during Sziget music festival on an island in the Danube River in Budapest, Hungary August 12, 2015. (Photo by Laszlo Balogh/Reuters)

Revellers relax inside a 3-D Luminarium inflatable installation by British designer Alan Parkinson during Sziget music festival on an island in the Danube River in Budapest, Hungary August 12, 2015. (Photo by Laszlo Balogh/Reuters)

Revellers relax inside a 3-D Luminarium inflatable installation by British designer Alan Parkinson during Sziget music festival on an island in the Danube River in Budapest, Hungary August 12, 2015. (Photo by Laszlo Balogh/Reuters)

A couple play in foam during the Sziget music festival on an island in the Danube River in Budapest, Hungary August 12, 2015. (Photo by Laszlo Balogh/Reuters)

Revellers play in foam during the Sziget music festival on an island in the Danube River in Budapest,Hungary August 12, 2015. (Photo by Laszlo Balogh/Reuters)

Revellers cool themselves by the Danube River during the Sziget music festival on an island in Budapest, Hungary August 12, 2015. A heatwave has hit Hungary with temperatures topping 38 degrees Celsius (100 degrees Fahrenheit). (Photo by Laszlo Balogh/Reuters)

A festival-goer walks in an installation during the 23rd Sziget (Island) Festival on Shipyard Island in Budapest, Hungary, 11 August 2015. The event is one of the biggest cultural events of Europe, offering art exhibitions, theatrical and circus performances and music concerts. Almost 200 performers from 47 countries will entertain the hundreds of thousands of visitors from 11 to 18 August. (Photo by Balazs Mohai/EPA)

Revellers cool themselves off in the Danube River during the Sziget music festival on an island in Budapest, Hungary August 12, 2015. (Photo by Laszlo Balogh/Reuters)

Revellers cool themselves in the Danube River during the Sziget music festival on an island in Budapest, Hungary August 12, 2015. (Photo by Laszlo Balogh/Reuters)

Revellers cool themselves in the Danube River during the Sziget music festival on an island in Budapest, Hungary August 12, 2015. (Photo by Laszlo Balogh/Reuters)