Just four days before South America's first Summer Olympic Games, there's still widespread fear that Rio is unprepared to stage a global spectacle. There's a crime spree, corruption and shoddy construction of major venues. Water contamination is a threat to the health of swimmers and sailors. And the Russian doping scandal has cast doubt on the integrity of world-class athletics. We hear what all this means for the quality of the competition, the size of the crowds and rules for staging Olympiads of the future.