Book Shop - Problem Statement

You're in a book shop with $n$ books. Each book has a price and a number of pages. You have a budget of $x$. Buy books to get the highest total pages.

Sound familiar? This is 0/1 Knapsack wearing a disguise. $Budget = capacity$, $price = weight$, $pages = value$. Before reading on, try to map this problem to the knapsack framework you already know. Read the problem statement carefully, noting the constraints.