Serbia's Milorad Cavic (L-R), South Africa's Chad le Clos, Michael Phelps of the U.S. and Tyler McGill of the U.S. prepare to compete in the men's 100m butterfly final during the London 2012 Olympic Games at the Aquatics Centre August 3, 2012. REUTERS/Michael Dalder (BRITAIN - Tags: SPORT SWIMMING SPORT OLYMPICS)