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)

{-# LANGUAGE MultiWayIf #-}

import Control.Monad
import Data.Maybe (fromJust)
import qualified Data.ByteString.Char8 as B
import Data.IORef

main :: IO ()
main = do
    [w, h, n] <- map (fst . fromJust . B.readInt) . B.words <$> B.getLine :: IO [Int]
    x1 <- newIORef 0
    x2 <- newIORef w
    y3 <- newIORef 0
    y4 <- newIORef h
    replicateM_ n $ do
        [x, y, a] <- map (fst . fromJust . B.readInt) . B.words <$> B.getLine :: IO [Int]
        xx1 <- readIORef x1
        xx2 <- readIORef x2
        yy3 <- readIORef y3
        yy4 <- readIORef y4
        if  | a == 1 -> writeIORef x1 (max xx1 x)
            | a == 2 -> writeIORef x2 (min xx2 x)
            | a == 3 -> writeIORef y3 (max yy3 y)
            | a == 4 -> writeIORef y4 (min yy4 y)
    xxx1 <- readIORef x1
    xxx2 <- readIORef x2
    yyy3 <- readIORef y3
    yyy4 <- readIORef y4
    print $ max 0 (xxx2 - xxx1) * max 0 (yyy4 - yyy3)