Facebook's $1 billion acquisition of Instagram, the largest ever for the company, wasn't quite what the twentysomething cofounders of the photo-sharing site wanted. No, Kevin Systrom and Mike Krieger wanted more — $2 billion to be exact. Regarding the sale, Wall Street Journal report: "Negotiating mostly on his own, Mr. [Mark] Zuckerberg had fielded Mr. Systrom's opening number, $2 billion, and whittled it down over several meetings at Mr. Zuckerberg's $7 million five-bedroom home in Palo Alto. Later that Sunday, the two 20-somethings would agree on a sale valued at $1 billion."

The small company, which had just 13 employees and no revenue at the time of sale, was founded in 2010. After it launched in October, it had one million registered users by December of that year. Seeing it as a possible threat to Facebook, Zuckerberg and Systrom had a three-day meeting at Mark's Palo Alto home. Here's what went down:

The two CEOs began their talks Thursday night at Mr. Zuckerberg's remodeled, century-old home, and met there again Friday and Saturday, wrapping up with a 12-hour session on Sunday, people familiar with the matter said. Each night, Mr. Systrom drove back to his house in San Francisco, one of the people said.

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Now, however, Mr. Systrom found himself in Mr. Zuckerberg's house asking $2 billion for Instagram. Mr. Zuckerberg suggested looking at the value of Instagram as a percentage of the value of Facebook, people familiar with the matter said.

Mr. Zuckerberg, who planned to pay for Instagram mostly with stock, asked Mr. Systrom what he thought Facebook would be worth, the people said. If he believed Facebook would one day be worth as much as a company like Google at $200 billion or more, then the equivalent of 1% of Facebook would be sufficient to meet his price, Mr. Zuckerberg told Mr. Systrom, the people said.

Also, Zuckerberg didn't so much as consult with Facebook's board as he simply tell them that he planned on making the buy. After all, he owns 28% of Facebook's stock, while controlling 57% of its voting rights. He can pretty much do whatever he wants. Zuckerberg announced the sale on his Facebook page, explaining: "This is an important milestone for Facebook because it's the first time we've ever acquired a product and company with so many users. We don't plan on doing many more of these, if any at all. But providing the best photo sharing experience is one reason why so many people love Facebook and we knew it would be worth bringing these two companies together."