Croatian company Photomath which makes a mobile app that scans and solves mathematical equations secured $23 million in funding, company founder, Damir Sabol, said on Thursday.

Sabol made the announcement at an online press conference, adding that the latest round of funding came from investors in the Silicon Valley.

Photomath is a free app billed as “digital mathematics tutor” and helps users solve mathematical tasks. It has been downloaded 220 million times since its launch in 2014.

Math equations can be hand-written or typed up on a computer, which the app then scans using mobile phone cameras and solves them using artificial intelligence.

“This investment is very important for us and even though Photomath has still not become a “business unicorn,” market potential does exist. And even though it hasn’t been easy, we are on the right track,” Sabol said.

He said that him and other investors currently own “about 50 percent” of the company. Over seven years that the company has been developing the app, about $40 million has been invested into the company date, including the latest $23 million round of funding.

Sabol said that apart from the 220 million downloads around the world, about 10 million users actively use the application each month, adding that the market potential lies in about a billion students worldwide who learn math.

About 50 percent of app users are high school students, and about 20 percent elementary school pupils. The remaining 30 percent includes university students and teachers. About 7 percent are parents who use the app to help their children.

Photomath’s largest market is the United States where about a quarter of its users come from, followed by Russia (12 percent), and then Indonesia, Brazil, and Italy.