How can I get the leftover room space?

So this is the task I need help with:

The blueprint of a house is made on a unit square grid sheet. All rooms must be rectangular. So far, N rooms have been drawn on the blueprint. Each room is defined by the upper left and lower right corners. One field of the square grid is given by the x and y coordinates, the coordinates of the upper left field (0,0). The x-coordinates increase horizontally and the y-coordinates increase vertically. The designer wants to calculate how many new rectangular rooms can be added if the two sides of any two new rooms cannot have a common part, and all four sides are adjacent or existing, or the side of the house. The rooms planned so far are such that every free space is rectangular. Make a program that tells you what the largest possible new room area can be in your plan.

Input:

The first line of the standard input has the number of rooms in the design (1≤N≤10,000) and the coordinates of the upper left (FX, FY) and lower right (AX, AY) corners of the house (0≤FX

Output:

The first line of the standard output should be the area of ​​the largest new room!

Theres an example in the link and its the basic input and output that you can test the program with. I translated this task from hungarian so the Példa=example , Bemenet=input , Kimenet=output. I would be really happy to get some help with this taks because for me it is a little bit too hard.

Basic input example