Joy was fed up of his increasing weight. All the time he kept thinking of the ways to reduce his weight

One day he went to a shopkeeper and said, "I have come to know about a book that tells how to reduce weight. Please give me a copy of that book." The shopkeeper said, "Sir, the last copy of that book got sold just a few minutes back. But I have another book that tells how to gain weight." Joy said, "I don't need that. I want to reduce weight, not increase it." The shopkeeper replied, " So what? Just do the reverse of what is written in the book."