#include <stdio.h>

int width, height, queens;
char pole[20000][20000];
int i, j;

int max(int a, int b) {
  return (a > b)? a : b;
}

void zaznacit(int Qx, int Qy) {
  for (i = 0; i < width; i++)
    pole[i][Qy] = 1;

  for (i = 0; i < height; i++)
    pole[Qx][i] = 1;

  int status = 1;
  for (i = 0; i <= max(width, height); i++) {
    status = 0;
    if (Qx - i >= 0 && Qy - i >= 0) {
      pole[Qx - i][Qy - i] = 1;
      status = 1;
    }
    if (Qx + i < width && Qy - i >= 0) {
      pole[Qx + i][Qy - i] = 1;
      status = 1;
    }
    if (Qx + i < width && Qy + i < height) {
      pole[Qx + i][Qy + i] = 1;
      status = 1;
    }
    if (Qx - i >= 0 && Qy + i < height) {
      pole[Qx - i][Qy + i] = 1;
      status = 1;
    }
    if (status == 0) break;
  }
}

int main(void) {
  int counter = 0;
  int Qx, Qy;
  int k;

  scanf("%d %d %d\n", &width, &height, &queens);
  for (k = 0; k < queens; k++) {
    scanf("%d %d\n", &Qx, &Qy);
    Qx--; Qy--;
    /*if (strcmp("0 0 0", in) == 0)
      break;*/
    zaznacit(Qx, Qy);
  }

  for (i = 0; i < width; i++) {
    for (j = 0; j < height; j++) {
      if (pole[i][j] == 0)
        counter++;
      /*printf("%d ", pole[i][j]);*/
    }
    /*printf("\n");*/
  }

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

  return 0;
}