Notebook Counting

Chef has $A$ notebooks with him, each having a total of $B$ pages. Each page has $50$ lines drawn to be written on, and you can write on both sides of the pages. Chef has to follow the drawn lines when writing. Thus, he can only write $50$ lines on the front side of the page, and $50$ lines on the back side. What is the effective total number of lines that Chef can write across all his notebook