Problem:
Score : 200 points

Problem Statement

There is a rectangle in the xy-plane, with its lower left corner at (0, 0) and its upper right corner at (W, H). Each of its sides is parallel to the x-axis or y-axis. Initially, the whole region within the rectangle is painted white.

Snuke plotted N points into the rectangle. The coordinate of the i-th (1 ≦ i ≦ N) point was (x_i, y_i).

Then, he created an integer sequence a of length N, and for each 1 ≦ i ≦ N, he painted some region within the rectangle black, as follows:

If a_i = 1, he painted the region satisfying x < x_i within the rectangle.

If a_i = 2, he painted the region satisfying x > x_i within the rectangle.

If a_i = 3, he painted the region satisfying y < y_i within the rectangle.

If a_i = 4, he painted the region satisfying y > y_i within the rectangle.

Find the area of the white region within the rectangle after he finished painting.

Constraints

1 ≦ W, H ≦ 100

1 ≦ N ≦ 100

0 ≦ x_i ≦ W (1 ≦ i ≦ N)

0 ≦ y_i ≦ H (1 ≦ i ≦ N)

W, H (21:32, added), x_i and y_i are integers.

a_i (1 ≦ i ≦ N) is 1, 2, 3 or 4.

Input

The input is given from Standard Input in the following format:

W H N
x_1 y_1 a_1
x_2 y_2 a_2
:
x_N y_N a_N

Output

Print the area of the white region within the rectangle after Snuke finished painting.

Sample Input 1

5 4 2
2 1 1
3 3 4

Sample Output 1

9

The figure below shows the rectangle before Snuke starts painting.

First, as (x_1, y_1) = (2, 1) and a_1 = 1, he paints the region satisfying x < 2 within the rectangle:

Then, as (x_2, y_2) = (3, 3) and a_2 = 4, he paints the region satisfying y > 3 within the rectangle:

Now, the area of the white region within the rectangle is 9.

Sample Input 2

5 4 3
2 1 1
3 3 4
1 4 2

Sample Output 2

0

It is possible that the whole region within the rectangle is painted black.

Sample Input 3

10 10 5
1 6 1
4 1 3
6 9 4
9 4 2
3 1 3

Sample Output 3

64

Solution in Haskell (GHC 7.10.3) (judge verdict: Accepted)

import Control.Monad                                                                                                       
                                                                                                                           
main :: IO ()                                                                                                              
main = do                                                                                                                  
  [w,h,n] <- map read . words <$> getLine                                                                                  
  xyas <- replicateM n $ map read . words <$> getLine :: IO [[Int]]                                                        
  let xyat = zip3 (map (!!0) xyas) (map (!!1) xyas) (map (!!2) xyas)                                                       
      x1 = maximum . (0:) . map fst3 . filter ((==) 1 . thd3) $ xyat                                                       
      x2 = minimum . (w:) . map fst3 . filter ((==) 2 . thd3) $ xyat                                                       
      y1 = maximum . (0:) . map snd3 . filter ((==) 3 . thd3) $ xyat                                                       
      y2 = minimum . (h:) . map snd3 . filter ((==) 4 . thd3) $ xyat                                                       
  print $ (max (x2 - x1) 0) * (max (y2 - y1) 0)                                                                            
                                                                                                                           
fst3,snd3,thd3 :: (a,a,a) -> a                                                                                             
fst3 (x,_,_) = x                                                                                                           
snd3 (_,y,_) = y                                                                                                           
thd3 (_,_,z) = z