U.S. President Barack Obama, left, walks away after shaking hands with Russia’s President Vladimir Putin, right, during arrivals for the G-20 summit at the Konstantin Palace in St. Petersburg, Russia on Thursday, Sept. 5, 2013. The threat of missiles over the Mediterranean is weighing on world leaders meeting on the shores of the Baltic this week, and eclipsing economic battles that usually dominate when the G-20 world economies meet. (AP Photo/Alexander Zemlianichenko)