Statement

Alice decided to create a piece of modern art. She has N squares, numbered from 0 to N-1. She placed them along the x axis, such that their centers lie on the x axis. The sides of the squares are parallel to the x and y axes. Some squares may overlap. For each square i, Alice tells you the x coordinate X_i of its center, and the distance R_i between its center and its sides. Please note that the side length of square i is 2R_i. For example, the square with X=4 and R=3 is colored in red, and the square with X=8 and R=2 is colored in orange in the above figure. Your task is to compute the total area covered by Alice's N squares.