(L-R) Slovakia's Prime Minister Robert Fico, Finland's Prime Minister Juha Sipila, Swedens's Prime Minister Stefan Lofven and Lithuania's President Dalia Grybauskaite arrive to pose for a family photo during the European Union summit- the first one since Britain voted to quit- in Bratislava, Slovakia, September 16, 2016. REUTERS/Leonhard Foeger

European Union leaders pose for a family photo during the European Union summit- the first one since Britain voted to quit- in Bratislava, Slovakia, September 16, 2016. REUTERS/Leonhard Foeger

Greece's Prime Minister Alexis Tsipras (C), Germany's Chancellor Angela Merkel and Portugal's Prime Minister Antonio Costa (R) arrive to pose for a family photo during the European Union summit- the first one since Britain voted to quit- in Bratislava, Slovakia, September 16, 2016. REUTERS/Leonhard Foeger

Hungary's Prime Minister Victor Orban arrives to pose for a family photo during the European Union summit- the first one since Britain voted to quit- in Bratislava, Slovakia, September 16, 2016. REUTERS/Leonhard Foeger

A stands outside Fannie Mae headquarters in Washington February 21, 2014. REUTERS/Kevin Lamarque

Elon Musk, Chairman of SolarCity and CEO of Tesla Motors, speaks at SolarCity's Inside Energy Summit in Manhattan, New York October 2, 2015. REUTERS/Rashid Umar Abbasi/File Photo

U.S. President Barack Obama speaks at the Our Ocean Conference at the State Department in Washington, D.C., U.S., September 15, 2016. REUTERS/Kevin Lamarque

Burkina Faso's President Blaise Compaore poses during an European Union (EU)-Africa summit in Brussels April 2, 2014. REUTERS/Francois Lenoir