NEW YORK (MarketWatch) -- Warren Buffett told CNBC Monday that he wouldn't sell stocks Monday because of the crisis in Ukraine. If anything, the chief executive of Berkshire Hathaway Inc. BRK.A, +0.36% BRK.B, +0.07% said in an interview, he would be a buyer. "If we get into a major war, the value of money goes down, so the last thing you'd want to do is hold money," Buffett said. "The stock market is going to advance over time. You are going to be a lot better off holding productive assets over the next 50 years." Separately, he described the controversial Keystone pipeline as "probably a good idea for the country."