SPOJ Problem Set (partial)
2211. Mars Map
Problem code: NKMARS

(This task was inspired by task ‘Atlantis’ of the Mid–Central European Regional ACM–ICP Contest 2000/2001.)
In the year 2051, several Mars expeditions explored different areas of the red planet and produced maps of these areas.
Now, the BaSA (Baltic Space Agency) has an ambitious plan: they would like to produce a map of the whole planet. In
order to calculate the necessary effort, they need to know the total size of the area for which maps already exist. It is your
task to write a program that calculates this area.
Input
The input starts with a line containing a single integer N (1 ≤ N ≤ 10 000 ), the number of available maps. Each
of the following N lines describes a map. Each of these lines contains four integers x_{1}, y_{1}, x_{2} and y_{2} (0 ≤ x_{1} < x_{2} ≤ 30 000 ,
0 ≤ y_{1} < y_{2} ≤ 30 000 ). The values ( x_{1};y_{1}) and ( x_{2};y_{2}) are the coordinates of, respectively, the bottomleft and the top
right corner of the mapped area. Each map has rectangular shape, and its sides are parallel to the x and yaxis of the
coordinate system.
Output
The output should contain one integer A, the total area of the explored territory (i.e. the area of the union
of all the rectangles).
Example
Input
2
10 10 20 20
15 15 25 30
Output
225
Added by:  Duc 
Date:  20071215 
Time limit:  1s

Source limit:  50000B 
Memory limit:  256MB 
Cluster: 
Pyramid (Intel Pentium III 733 MHz)

Languages:  All except: ERL JS NODEJS PERL 6 
Resource:  Baltic OI 2001 
