U.S. President George W. Bush and Russian President Vladimir Putin failed to resolve their differences over a U.S. missile defense system at a farewell meeting on Sunday. Bush insisted the system to be built in Eastern Europe is not aimed at Russia and that people must accept that «the Cold War is over.» Putin said he's cautiously optimistic that Russia and the U.S. will find a way to cooperate on missile defense but there was a long way to go. «Our countries still have serious disagreements on certain problems,» Putin was quoted as saying by the Associated Press. Bush also met Putin's successor Dmitry Medvedev and pronounced him «a straightforward fellow.» «You can write down, I was impressed and look forward to working with him,» Bush told reporters after meeting Medvedev. Putin, who steps down on May 7 to become prime minister, said Medvedev would then determine foreign policy and represent Russia at this year's Group of Eight meeting of world economic powers.