# Problem: Election

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## Election

**Input File:** `elecin.txt`

**Output File:** `elecout.txt`

**Time Limit:** 1 second

Election time is coming around, and you are lagging in the polls. Your
highly-paid advisors have told you that the surest way to be re-elected
is to hang an incredibly large picture of your face outside the front of
the town hall — the larger the picture, the greater the votes!

You step outside and survey the front wall of the building. The wall
forms a giant rectangle, containing several small rectangular windows.
You cannot block anybody's view (this would surely cause a scandal), so
your task is to find a rectangle on this wall with the largest possible
area that does not cover any part of a window.

As an example, consider the wall illustrated above. The diagram on the
left shows three windows on the wall, shaded in black. The diagram on
the right shows the rectangle of largest area that you can use, shaded
in grey.

### Input

The first line of input will contain the integers *w* and *h*
separated
by a single space, where *w* is the width of the wall and
*h* is the
height of the wall
(1 <= *w*,*h* <= 40,000).
The second line of input will contain the single integer *n*, describing
the number of windows in this wall
(0 <= *n* <= 100).

Following this will be *n* lines, each describing a single window.
The *i*th of these lines will be of the form
*x*_{i} y_{i} w_{i} h_{i},
where
*x*_{i} is the distance of the window from the leftmost
edge of the wall,
*y*_{i} is the distance of the window from the bottom
edge of the wall,
*w*_{i} is the width of the window, and
*h*_{i} is the height
of the window. These distances are illustrated below.

For each window, the four integers
*x*_{i} y_{i} w_{i} h_{i}
will be separated by single spaces.
It is guaranteed that
1 <= *x*_{i} < *x*_{i} + *w*_{i} <= *w* and
1 <= *y*_{i} < *y*_{i} + *h*_{i} <= *h*.
No two windows will overlap, although windows may touch at a corner
or along an edge.

All distances are measured in centimetres.

### Output

Your output must consist of a single line containing a single integer,
giving the area of the largest possible rectangle on the wall that does
not cover any part of a window. This area should be given in
square centimetres.

### Sample Input

800 600
3
100 250 100 150
150 180 450 20
400 500 50 50

### Sample Output

180000

### Explanation

The sample data above describes the example that was illustrated
earlier. The rectangle of largest area that does not cover any part of
a window has width 600 and height 300, and so the final area is
600 x 300 = 180,000.

### Scoring

The score for each input file will be 100% if the
correct answer is written to the output file and 0% otherwise.