SAINT PETERSBURG - SEPTEMBER 06: Russian President Vladimir Putin, Brazilian President Dilma Rousseff, US President Barack Obama, British Prime Minister David Cameron, German Chancellor Angela Merkel and other leaders pose for a group photo during the G20 summit on September 6, 2013 in St. Petersburg, Russia. Leaders of the G20 nations made progress on tightening up on multinational company tax avoidance, but remain divided over the Syrian conflict during the final day of the Russian summit. (Photo by Sasha Mordovets/Getty Images)

SAINT PETERSBURG - SEPTEMBER 06:  Russian President Vladimir Putin, Brazilian President Dilma Rousseff, US President Barack Obama, British Prime Minister David Cameron, German Chancellor Angela Merkel and other leaders pose for a group photo during the G20 summit on September 6, 2013 in St. Petersburg, Russia.  Leaders of the G20 nations made progress on tightening up on multinational company tax avoidance, but remain divided over the Syrian conflict during the final day of the Russian summit.   (Photo by Sasha Mordovets/Getty Images)