What's the market value of a Pokémon game that Nintendo's parent company only kinda sorta controls and publishes? About $9 billion.

That's how much value Nintendo's stock has gained since last Wednesday, with the shares shooting up 25% on Monday alone. In total, they have risen by almost 40% since the release of Pokémon Go, reflecting investors' glee at Nintendo finally using its beloved characters and intellectual property to make a hit mobile game.

The gaming giant has largely sat out the mobile era, focusing instead on making games for its own consoles. But now that is has a smash hit on its hands — one that sits atop the iOS App Store for free and top-grossing apps despite bugs, connectivity issues, alleged armed robberies, and one Wyoming teen finding a dead body while playing it. Nintendo was valued at almost $28 billion on Monday afternoon.

But the company won't be collecting all the money generated by Pokémon Go. Instead, it owns stakes in both the Pokémon Company and Niantic, the game's developer, which spun out from Google's parent company Alphabet last year.

Analysts at the Japanese investment bank Nomura said that the huge surge in Nintendo's stock price "looks excessive based on profits from Pokémon Go alone," which they estimated to be only about $10 to $20 million annually for Nintendo itself.