Book on Memory

A person was weak in memory. He sees a book in shop " Sure techniques of increasing memory" He buys and reads continuously for 4 days. he is very impressed with the techniques. After finishing the book he is shouting with excitement that his problem is surely solved and now he has fantastic memory. He goes to keep this book in his Almira and to his utter shock, he finds another copy of same book lying in the Almira ( which he has read 15 days ago!)