It's no surprise that all 500 pairs of the limited edition sneakers flew off the shelves. People lined up days in advance to secure a chance at buying a pair, à la Ikea.

The shoes? Adidas EQT Support 93/Berlin.

The allure? These sneakers have a fabric Berlin transit card stitched into the tongues. It's valid for an annual pass across the A and B zones on Berliner Verkehrsbetriebe (BVG), Berlin's public transportation company.

The equivalent annual pass costs about $931. The sneakers -- free annual pass included -- cost just €180, or $220. If you got your hands on a pair and use Berlin's trains, buses and trams to get around, these were a steal.

Public transportation riders don't need to scan their feet to enter the subway or hop on a bus. Berlin has controller who check riders' validated tickets. If you're sporting a pair of the Adidas EQT Support 93/Berlins, all you have to do is point to your feet. For your "ticket" to be valid, you must be wearing both shoes.

But now for the bigger question: Why exactly did Adidas make these sneakers? It's part of a collaboration with BVG. BVG wants to communicate the message that riding public transportation is cool, according to a piece in The Guardian. They're hoping this move boosts ridership among younger people.

The sewn-in BVG transit card is just one design element of these sneakers. They also feature the black, blue and red camouflage pattern from BVG's train seats. A small yellow heart stitched onto the side represents BVG logo.

The translated tweet reads: "Yes, these are sneakers in the BVG design. Yes, they are valid as an annual ticket. No, you can't put them on the seat." (Even though one picture features someone putting their feet on the seat.)

"The motivation behind the collaboration is really to get young people on to public transport," BVG spokesperson Petra Reetz told The Guardian, "We wanted to tell young people public transport is cool - you don't need to buy a car."