Citigroup ( C) posted first-quarter profit of $1.6 billion versus a loss the year before, but before you celebrate you should check what kind of stock you own.

If you're a preferred shareholder, say like the U.S. government, then you're in the money!

If you're a common shareholder, then you get nothing. Actually, you get less than nothing. You get a loss of 18 cents a share.

After cutting out $1.3 billion to reset the conversion price of preferred stock issued in January 2008, paying another $1.3 billion in preferred dividends and booking a cost of $53 million related to participation in the government's Troubled Asset Relief Program, Citigroup's profit turned into a net loss of $966 million.

That's not the headline number, but it's the real number. Citi can talk all it wants about posting a net income, but the reality for ordinary shareholders is the company lost money. That is the bottom line.

Now I'm not saying there's nothing to like about Citi's earnings. The $9.5 billion in revenue and $2.8 billion in profit from the institutional clients group in the first quarter is encouraging, especially considering the bank posted a $6.4 billion loss from those operations the year before. That's the bright spot.

There are also some dark spots, such as the $13.1 billion in write downs, which include almost $7 billion related to bad subprime and Alt-A mortgages and $3 billion for "highly leveraged finance commitments."

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