There are 100,000 free books up for grabs at a former pub in north London. You can take as many as you want. So how many do you think are left after three months?
It turns out that about 90,000 books of all genres remain at the Free Bookshop in Islington where The Kindness Offensive (TKO) set up its bookshop in October, as one of many random acts of kindness it carries out across the capital.
It offered 100,000 books to anyone who wanted them and invited people to donate books if they wanted to - but there was no obligation.
Organiser David Goodfellow said: "It's going from strength to strength.
"The local community have been bringing books in every day and at least twice a week we take receipt of entire book collections.
"This has meant that we have not had to dip into our store of books as deeply as we thought."
The bookshop is run entirely by volunteers for 40 hours a week, 10 hours more than TKO had originally anticipated.
Made up of old and new books, many have been given a second life after being diverted from landfill.
Mr Goodfellow said: "The oldest book we've found is around 150 years old and was an illustrated botany reference book with hand-drawn images. That's gone now, but the newest we found was a pre-release."
The three-month marker comes just after Christmas, the same time thousands of people around the country will be frantically fighting to get their hands on the best sale items at high street shops across the country.
So why the restraint at a shop which actually offers something for nothing?
Dr Gareth Harvey, a lecturer in consumer psychology at Wrexham's Glyndwr University, said the seeming restraint might not be down to charitable goodwill, but more to do with the way people view "free".
He said: "There's often a stigma attached. If you're seen there, people will assume you're quite tight.
"At a charity shop, you've lost the stigma because you're getting something for virtually nothing but you're doing something good for someone else.
"But once you've made that first purchase you're more likely to pick up multiple items."
Mr Goodfellow said there are customers who have "become regulars" with one man building up his own private library three books at a time.
But he added: "We get the sense that most people understand that it's a community project and as a result they take part at a sustainable level."
Director of Customer Psychology Ltd Gareth English said the origins of the books would also impact on people's actions.
He said: "Because everything in the shop is free it changes everyone's mentality.
"If you set up in Waterstones I bet those free books would fly off the shelf, but these guys are doing everything free so it changes our minds and unlocks the nicer bits of us."
Psychologically speaking, if people can be reserved when it comes to free items, why is there such a panic when it comes to Christmas shopping or the post-Christmas sales?
Dr English said: "If it's expected for people to buy lots at Christmas, that's what we end up doing. We judge normal by what we see other people doing."
There are many factors which will determine how long the Free Bookshop remains open, including how long it is permitted to use the pub, how long local businesses want to keep paying the rent and, of course, how long the books last.
But at this rate the book supply could last until October 2014.
Mr Goodfellow said: "People are regularly amazed at the idea of free books and walk around our colourful shop wide-eyed.
"We have become something of a local attraction."