Citigroup ( (C) - Get Report ) shares are undervalued, which means it's a good time to buy the stock. TheStreet's Jim Cramer just opened a position on the stock, adding that this is the bank "we want to put more money in."

Shares are floating around $46.66 in early afternoon trading, at around a .75 discount to tangible book value. Given the big disparity between its share price and tangible book value, it's time to "move into that," Cramer said.

Citigroup shares should increase to trade near its tangible book value in the 18 to 24 month time frame, Rafferty Capital Markets analyst Richard Bove said. Citigroup's results for the second half of the year should pick up meaningfully, he explained. He has a "buy" recommendation on the stock, in part because of what Bove says is it's safe capital structure.

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"The company has made strides in terms of reducing riskiness of the enterprise" and is "far better capitalized than it has been in a long time," a second industry analyst said.

Cramer credits Citigroup CEO Michael L. Corbat, who he says has done a great job, while the second analyst explained that "the senior management team continues to make rational decisions about where they want to place their resources." Corbat took over the reigns as CEO in 2012.

The bank was a big winner last month, when the Federal Reserve and the Federal Deposit Insurance found the bank's living will to credible, in contrast to those or Bank of America (BAC), Bank of New York Mellon (BK), JPMorgan Chase (JPM), State Street (STT) and Wells Fargo (WFC).

The bank reported net income of $3.5 billion, or $1.10 per diluted share, for the first quarter of 2016, compared with net income of $4.8 billion, or $1.51, for last year's first quarter, on revenues of $17.6 billion, compared with $19.7 billion for the year-earlier period.

Citigroup shares are down around 5% year-to-date. The bank has a market cap of $135 billion.