Maurice Levy, chief executive officer of Publicis Groupe SA, left, and John Wren, chief executive officer of Omnicom Group Inc., shake hands on the merger deal during a news conference held on the rooftop of the Publicis headquarters in Paris, France, on Sunday, July 28, 2013.Publicis Groupe SA and Omnicom Group Inc. agreed to merge in an all-stock transaction to create the worldÕs largest advertising company with $23 billion in revenue,toppling market leader WPP Plc. Photographer: Balint Porneczi/Bloomberg *** Local Caption *** Maurice Levy; John Wren