NKMARS  Mars Map
English  Vietnamese 
(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
hide comments
Eddy Cael:
20180321 19:01:21
After several versions, finally, I did it... Good problem :) 

nikoo28:
20120729 17:54:40
can someone provide me with more test cases?? 
Added by:  Duc 
Date:  20071215 
Time limit:  1s 
Source limit:  50000B 
Memory limit:  1536MB 
Cluster:  Cube (Intel G860) 
Languages:  All except: ERL JSRHINO NODEJS PERL6 VB.NET 
Resource:  Baltic OI 2001 