By Matthew Prodger BBC News, Belgrade

Serbian football fans getting in touch with their inner child

Every Saturday and Sunday at 1700 a crowd gathers at a fountain outside Belgrade's landmark Hotel Moscow.

Sometimes there are a few dozen, on other occasions hundreds of people.

It looks like a street market, but there are no stalls.

It sounds like an old-fashioned trading floor, but the assets changing hands here with such intensity are not of the financial kind.

The people of Belgrade are swapping football stickers - thousands of them.

Schoolchildren across the globe have been familiar with this World Cup ritual for years.

They spend their pocket money on packets of stickers emblazoned with the images of the competitors in this year's tournament.

Collector's item

The idea is to stick the pictures in an album in a race to complete every team in the world cup.

Every weekend crowds gather near Belgrade's Hotel Moscow

But finding all the players to finish the book is almost impossible unless you swap those you have a surplus of for those you need. And that is what is happening here every weekend.

What marks Belgrade apart is that these are not in the main schoolchildren, they are adults.

People like Dalibor Toskovic, 27, sporting dreadlocks, a football shirt, and a wedding ring. His wife, incidentally, is also swapping football stickers.

Dalibor is having a good day. He tells me with a huge beam that he has just completed the Argentine team, and finally tracked down a hard-to-find sticker of Switzerland's Philippe Senderos.

"This is all about nostalgia for childhood'' he says, clutching a pile of stickers as thick as two packs of cards. "I've filled every album since Mexico '86."

Is he tempted to sell what are fast becoming collector's items? "Never. No price would be enough."

Like a mating ritual

Another man boasts that he could get hundreds of euros for his collection on the auction website eBay.

It's important to stay young as long as possible and this is something from your childhood that you can continue throughout life Milos Saranovic

People wander around the fountain calling out the names of players they need, seeking a reply from those who can provide them.

It is a little like a mating ritual.

Milos Saranovic, a sports journalist with the Serbian TV station B92, is here with his young son, hunting for Serbia and Montenegro's striker Nikola Zigic.

"Collecting football stickers is a very important part of every World Cup," he says.

"It's important to stay young as long as possible and this is something from your childhood that you can continue throughout life. But it's a bit strange seeing men in their 30's and 40's swapping stickers and acting like kids."

Expensive hobby

Next to him a boy no older than seven is negotiating with three men towering over him. He is bargaining hard, demanding five stickers for the one they want.

The hobby can cost more than a third of the average monthly wage

By the end of the day Milos and his son have completed their albums.

"The job is done," he says. "Now we can prepare for Germany."

But for most people in Serbia and Montenegro a ticket to the World Cup is a distant dream.

Getting a visa is one problem - paying for the trip and entry to a game is another. This is not a wealthy country.

Even the hobby of collecting stickers can cost more than a third of the average monthly wage here.