The headquarters of Germany's Deutsche Bank is photographed early evening in Frankfurt, Germany, January 26, 2016. REUTERS/Kai Pfaffenbach/File Photo

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

Hungary's Prime Minister Victor Orban (L), Germany's Chancellor Angela Merkel and Austria's Chancellor Christian Kern (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

European Union countries flags are seen at the Bratislava Castle (Hrad) during the European Union summit- the first one since Britain voted to quit- in Bratislava, Slovakia, September 16, 2016. REUTERS/Yves Herman

European Union countries flags are seen at the Bratislava Castle (Hrad) during the European Union summit- the first one since Britain voted to quit- in Bratislava, Slovakia, September 16, 2016. REUTERS/Yves Herman

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

(L-R) Greece's Prime Minister Alexis Tsipras, Netherlands' Prime Minister Mark Rutte, France's President Francois Hollande and European Commission President Jean Claude Juncker attend the European Union summit- the first one since Britain voted to quit- in Bratislava, Slovakia, September 16, 2016. REUTERS/Yves Herman

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