#include <stdio.h>

int main(){
	int size_x,size_y,num_Q;
	bool ** pole;
	int queen_y,queen_x;
	int i;
	int obsazeno = 0;
	while( scanf("%d%d%d", &size_x, &size_y, &num_Q ) == 3 && size_y > 0 && size_x > 0 && num_Q >= 0 ){
		pole = new bool*[size_y];
		for( i=0 ; i<size_y ; i++ ){
		  pole[i] = new bool[size_x];
		}
		for(int k = 0; k < size_y; k++){
			for(int l = 0; l < size_x; l++){
				pole[k][l] = 0;
			}
		}
		for(int i = 0; i < num_Q; i++){
			scanf("%d %d", &queen_y, &queen_x);
			queen_y--; queen_x--;
			pole[queen_y][queen_x] = 1;
			for(int n = queen_y; n >= 0; n--){
				pole[n][queen_x] = 1;
			}
			for(int n = queen_y; n < size_y; n++){
				pole[n][queen_x] = 1;
			}
			for(int n = queen_x; n >= 0; n--){
				pole[queen_y][n] = 1;
			}	
			for(int n = queen_x; n < size_x; n++){
				pole[queen_y][n] = 1;
			}
			for(int x = 0; ; x++){
				if(queen_y-x < 0) break;
				if(queen_x+x == size_x) break;
				pole[queen_y-x][queen_x+x] = 1;
			}		
			for(int x = 0; ; x++){
				if(queen_y+x == size_y) break;
				if(queen_x+x == size_x) break;
				pole[queen_y+x][queen_x+x] = 1;
			}	
			for(int x = 0; ; x++){
				if(queen_y+x == size_y) break;
				if(queen_x-x < 0) break;
				pole[queen_y+x][queen_x-x] = 1;
			}	
			for(int x = 0; ; x++){
				if(queen_y-x < 0) break;
				if(queen_x-x < 0) break;
				pole[queen_y-x][queen_x-x] = 1;
			}	
		}
		for(int k = 0; k < size_y; k++){
			for(int l = 0; l < size_x; l++){
				if(pole[k][l] == 0) obsazeno++;
			}
		}
		printf("%d\n", obsazeno);
	}
	return 0; 
}