#include <stdio.h>
#define MAX 41000

int r[MAX];
int s[MAX];
int da[MAX];
int db[MAX];

int main()
{
	while (1)
	{
		int pocet = 0;
		int X,Y,N;
		scanf("%d %d %d", &X, &Y, &N);
		if (X == 0)
			return 0;
		for (int i = 0; i < MAX; i++)
		{
			r[i] = s[i] = da[i] = db[i] = 0;
		}
		for (int i = 0; i < N; i++)
		{
			int x,y;
			scanf("%d %d", &x, &y);
			x--; y--;
			
			s[x] = 1;
			r[y] = 1;
			da[x+y] = 1;
			db[x-y+20500] = 1;
		}

		/*for (int i = 0; i < X; i++)
		{
			printf("s[%d] = %d, ", i, s[i]);
		}
		printf("\n");
		for (int i = 0; i < Y; i++)
		{
			printf("r[%d] = %d, ", i, r[i]);
		}
		printf("\n");
		for (int i = 0; i < X+Y; i++)
		{
			printf("da[%d] = %d, ", i, da[i]);
		}
		printf("\n");
		for (int i = 20500-Y; i < 20500+X; i++)
		{
			printf("db[%d] = %d, ", i, db[i]);
		}
		printf("\n");*/

		for (int x = 0; x < X; x++)
		{
			for (int y = 0; y < Y; y++)
			{
				if (r[y] == 0 && s[x] == 0 && da[x+y] == 0 && db[x-y+20500] == 0)
				{
					pocet++;
					//printf("(%d, %d), ", x+1, y+1);
				}
			}
		}
		printf("%d\n", pocet);
	}
	return 0;
}