John walks into the daily grocery shop and steals a $100 bill from the shop. An hour later John returns to the shop and buys some daily products for $40. John pays the owner the $100 bill and therefore the owner returns him $60.
In 2007, a puzzle was released and $2 million prizes were offered for the first complete solution. The competition ended at noon on 31 December 2010, with no solution being found. Wiki