#include <stdio.h>
#include <stdlib.h>

int main(void) {
	long w, h, n, s, k, a, b, c;
	int sum = 0;
	int** card;

	scanf("%d", &w);
	scanf("%d", &h);
	scanf("%d", &n);

	card = (int**)malloc(sizeof(int*) * w);
	for (b = 0; b < w; b++)
		card[b] = (int*)malloc(sizeof(int) * h);

	for (b = 0; b < w; b++)
		for (c = 0; c < h; c++)
			card[b][c] = 0;

	for (a = 0; a < n; a++) {
		scanf("%d %d", &s, &k);
		for (b = 0; b < w; b++) {
			for (c = 0; c < h; c++) {
				if (b == s - 1 && c == k - 1)
					card[b][c] = 2;
				else if (card[b][c] != 2) {
					if (b == s - 1 && c != k - 1)
						card[b][c] = 1;
					if (b != s - 1 && c == k - 1)
						card[b][c] = 1;
				}
			}
		}
	}

	for (b = 0; b < w; b++)
		for (c = 0; c < h; c++)
			if (card[b][c] == 1)
				sum += card[b][c];

	printf("%d\n", sum);

	for (b = 0; b < w; b++)
		free(card[b]);
	free(card);

	return EXIT_SUCCESS;
}