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 C (Clang 3.8.0) (judge verdict: Accepted)

// ABC047 B - すぬけ君の塗り絵 2 イージー
#include <stdio.h>

int main(void)
{
    int W, H, N;

    scanf("%d %d %d", &W, &H, &N);

    int S[N][3];
    int i = 0;
    for (i = 0; i < N; i++) {
        scanf("%d %d %d", &S[i][0], &S[i][1], &S[i][2]);
    }

    int xStart = 0, xEnd = W, yStart = 0, yEnd = H;
    for (i = 0; i < N; i++) {
        switch (S[i][2]) {
        case 1:
            if (xStart < S[i][0]) {
                xStart = S[i][0];
            }
            break;
        case 2:
            if (xEnd > S[i][0]) {
                xEnd = S[i][0];
            }
            break;
        case 3:
            if (yStart < S[i][1]) {
                yStart = S[i][1];
            }
            break;
        case 4:
            if (yEnd > S[i][1]) {
                yEnd = S[i][1];
            }
            break;
        default:
            break;
        }
    }
    
    int result = (xEnd - xStart) * (yEnd - yStart);
    if (xEnd <= xStart || yEnd <= yStart) {
        result = 0;
    }

    printf("%d\n", result);
    return 0;
}