A woman holds up a sign that reads "Ayotzinapa lives - 43 are missing" next to pictures of the 43 missing students of Ayotzinapa College on a police fence outside the Casa Rosada Presidential Palace during a protest against the visit to Argentina by Mexico's President Enrique Pena Nieto, in Buenos Aires, Argentina, July 29, 2016. REUTERS/Marcos Brindicci