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 Ruby (2.3.3) (judge verdict: Accepted)

w, h, n = gets.chomp.split(" ").map{|i| i.to_i}
x, y, a = Array.new(3){Array.new(n)}
for i in 0...n
    x[i], y[i], a[i] = gets.chomp.split(" ").map{|i| i.to_i}
end

field = Array.new(w){Array.new(h){false}}

def ok(i, j, _x, _y, a)
  case a
  when 1
    if i < _x
      true
    else
      false
    end
  when 2
    if i >= _x 
      true
    else
      false
    end
  when 3
    if j < _y
      true
    else
      false
    end
  when 4
    if j >= _y
      true
    else
      false
    end
  end
end

for k in 0...n
  for i in 0...w
    for j in 0...h
      if ok(i, j, x[k], y[k], a[k])
        field[i][j] = true
      end
    end
  end
end

ans = 0
for i in 0...w
  for j in 0...h
    if field[i][h-1-j]
      #print "x"
    else
      #print "."
      ans += 1
    end
  end
  #print "\n"
end
puts ans