#include <stdio.h>
#include <set>
using namespace std;

bool wasr[20005];
bool wasc[20005];
bool wasd1[40005];
bool wasd2[40005];
int rr, cc, n, i, j, r, c;

inline int dajd1(int r, int c) {
	return (r-1)+(c-1);
}

inline int dajd2(int r, int c) {
	return (rr - r)+(c-1);
}

int main() {
	while (scanf("%d%d%d", &rr, &cc, &n), rr > 0) {
		for (i = 0; i < rr; i++) wasr[i] = false;
		for (i = 0; i < cc; i++) wasc[i] = false;
		for (i = 0; i < cc+rr; i++) wasd1[i] = wasd2[i] = false;
		while (n--) {
			scanf("%d%d", &r, &c);
			wasr[r-1] = true;
			wasc[c-1] = true;
			wasd1[dajd1(r,c)] = true;
			wasd2[dajd2(r,c)] = true;
		}
		int ret = 0;
		for (r = 1; r <= rr; r++) {
			for (c = 1; c <= cc; c++) {
				ret += !(wasr[r-1] || wasc[c-1] || wasd1[dajd1(r,c)] || wasd2[dajd2(r,c)]);
			}
		}
		printf("%d\n", ret);
	}
	return 0;
}