Hong Kong, July 2016.

Hundreds of high school students from around the world are gathered together for a global competition.

They're not competing in a foot race or on a football field.

Ladies and gentlemen, welcome to the opening ceremony of the 57th International Mathematico Olympics 2016.

The game here is Brainpower.

These youngsters are the cream of their country's math talent and this is one of the most prestigious competitions in the world.

The IQ count here is through the roof.

Over the next couple of days, they're going to compete to solve problems involving things like convex quadrilatials and no idea what that means either.

The name of all the participants we commit ourselves to honest conduct in the true sphere to fair play for the glory of mathematics and the honor of our teams.

I'm next, please join us in welcoming team Peoples Republic of China.

More than 100 countries are taking part and team members take to the stage to present themselves to the audience.

And yes, even one of the world's most reclusive countries has sent along a team.

I'm next, join us in welcoming team Democratic Peoples Republic of Korea.

Six young men step forward. They're teenagers really.

And while the rest of the competitors are in sweatpants, shorts and jeans, the North Koreans are in white dress shirts tucked neatly into black trousers.

They've got loyalty badges if the Kim's been carefully over their hearts and second from the left, one of them stands out.

He's slightly taller than the others. His name, Zhongyong-ri.

His team mates are smiling, but if you look closely, there's something going on with Zhongyong.

He's preoccupied. He keeps glancing to the side. He looks like he's in a hurry to get off the stage.

He's got something far more important than mathematics on his mind. It's freedom.

One year earlier, officials in North Korea had begun vetting his background and that of his family.

And they told him they had something in mind for his future.

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