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Warren Buffett's Berkshire Hathaway (BRK.A - Get Report)  notched it worst annual performance in nearly two decades last year, the famous investor revealed in a letter to shareholders over the weekend, but said he was still looking for an "elephant-sized acquisition" for the $173 billion investment fund.

Buffett said losses linked to his 26.7% investment in Kraft Heinz (KHC - Get Report) , as well as new accounting rules, contributed to a fourth quarter loss of around $25.4 billion, a figure that ate into an otherwise solid 2018 and reduced the net total gain to $4 billion, the weakest since 2001 and down 91% from the end of 2017. Buffett took a $3 billion hit on his Kraft stake as well as a "$20.6 billion loss from a reduction in the amount of unrealized capital gains that existed in our investment holdings" based on accounting rule changes that he said would likely result in "wide swings" in quarterly earnings going forward.

"Our prime goal in the deployment of your capital: to buy ably-managed businesses, in whole or part, that possess favorable and durable economic characteristics. We also need to make these purchases at sensible prices," Buffett said. "In recent years, the sensible course for us to follow has been clear: Many stocks have offered far more for our money than we could obtain by purchasing businesses in their entirety."

"That disparity led us to buy about $43 billion of marketable equities last year, while selling only $19 billion," he added. (Berkshire vice chairman Charlie Munger) and I believe the companies in which we invested offered excellent value, far exceeding that available in takeover transactions."

Buffett indicated a preference to investing and owing companies on a permanent basis with the $119.9 billion in cash that Berkshire is able to access, but lamented that "sky high" prices for such businesses likely means his fund will add to its holdings of marketable securities while continuing "to hope for an elephant-sized acquisition" that would "cause my pulse to soar."

Buffett also appeared to take aim at some of President Donald Trump's "America First" trade and economic policies, noting that it was "beyond arrogance for American businesses or individuals to boast that they have "done it alone."

"There are also many other countries around the world that have bright futures," Buffett argued. "About that, we should rejoice: Americans will be both more prosperous and safer if all nations thrive. At Berkshire, we hope to invest significant sums across borders."

In terms of Berkshire Hathaway's equity investments, Buffett's 5.4% stake in Apple Inc. (AAPL - Get Report) remains the most valuable, even with the 20% decline recorded over the fourth quarter of last $ear, at $40.271 billion. The fund's 9.5% stake in Bank of America (BAC - Get Report) is next at $22.642 billion while Buffett's 9.8% holding in Well Fargo (WFC - Get Report) , valued at $20.706 billion, comes in third.

Buffett's Kraft Heinz stake was valued at $14 billion at the end of 2018, but shares in the packaged food maker fell to a record low $34.95 each Friday after it revealed weaker-than-expected fourth quarter earnings, a $15.4 billion writedown of the value of is Kraft and Oscar Mayer business units and told investors that the Securities and Exchange Commission was looking into some of its accounting practices.