output_description: Print the area of the white region within the rectangle after Snuke finished
  painting.
  
  * * *
input_description: 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
attempt: w,h,n=[int(i) for i in input().split(' ')]
  x1,x2,y1,y2=0,w,0,h
  for i in range(n):
    x,y,a=[int(i) for i in input().split(' ')]
    if a==1:
      x1=max(x1,x)
    if a==2:
      x2=min(x2,x)
    if a==3:
      y1=max(y1,y)
    if a==4:
      y2=min(y2,y)
  print(max(0,(y2-y1)*(x2-x1))
problem_description: 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.
samples: [{"input": "5 4 2\n    2 1 1\n    3 3 4", "output": "9\n    \n\nThe figure below shows the rectangle before Snuke starts painting.\n\n![e19e673abcd0882783f635cce9d2f94d.png](https://atcoder.jp/img/abc047/e19e673abcd0882783f635cce9d2f94d.png)\n\nFirst, as (x_1, y_1) = (2, 1) and a_1 = 1, he paints the region satisfying x <\n2 within the rectangle:\n\n![f25cd04bbac23c4e5426d70511a9762f.png](https://atcoder.jp/img/abc047/f25cd04bbac23c4e5426d70511a9762f.png)\n\nThen, as (x_2, y_2) = (3, 3) and a_2 = 4, he paints the region satisfying y >\n3 within the rectangle:\n\n![46b0c06fd9eee4f148e1f441f7abca53.png](https://atcoder.jp/img/abc047/46b0c06fd9eee4f148e1f441f7abca53.png)\n\nNow, the area of the white region within the rectangle is 9.\n\n* * *"}, {"input": "5 4 3\n    2 1 1\n    3 3 4\n    1 4 2", "output": "0\n    \n\nIt is possible that the whole region within the rectangle is painted black.\n\n* * *"}, {"input": "10 10 5\n    1 6 1\n    4 1 3\n    6 9 4\n    9 4 2\n    3 1 3", "output": "64"}]