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BERLIN, GERMANY - DECEMBER 11: Contract cleaners stand on a glass roof and clean the surface with a scrubbing brush on December 11, 2014 in Berlin, Germany. (Photo by Michael Gottschalk/Photothek via Getty Images)

BERLIN, GERMANY - DECEMBER 11:  Contract cleaners stand on a glass roof and clean the surface with a scrubbing brush on December 11, 2014 in Berlin, Germany. (Photo by Michael Gottschalk/Photothek via Getty Images)