#include <stdio.h>

char cb[20001][20001]; 

int main()
{
    
    int N = 0;
    int cb_X = 0;
    int cb_Y = 0;
    while(scanf("%d %d %d", &cb_X, &cb_Y, &N)){
        int count = 0;
        for(int i=0; i<cb_Y; i++)
        {
            for(int a=0; a<cb_X; a++)
            {
                cb[i][a] = 0;
                //if(cb[i][a]=='x')
                //printf("%c  ",cb[i][a]);
                //else
                //printf("o  ");
            }  
            //printf("\n");
        }        
        if(cb_X == 0 && cb_Y == 0 && N == 0){
            return 0;
        }
        
        int vetsi = cb_X;
        if(cb_Y<vetsi){
            vetsi = cb_Y;
        }
        if(N >= (vetsi - 1)){
            printf("0\n");
        }else{
            for(int i = 0; i < N; i++){
                int q_x = 0;
                int q_y = 0;
                scanf("%d %d", &q_x, &q_y);    
                q_x = q_x-1;
                q_y = q_y-1;
                for(int x = 0; x < cb_X; x++){ //prochazeni x osou
                    if(cb[q_y][x] != 'x')
                    {
                        cb[q_y][x] = 'x';
                        count++;
                    }
                }
                for(int y = 0; y < cb_Y; y++){ //prochazeni y osou
                    if(cb[y][q_x] != 'x')
                    {
                        cb[y][q_x] = 'x';
                        count++;
                    }
                }
                if(q_y<q_x)
                {
                    int pomX = q_x-q_y;
                    for(int y=0;y < cb_Y;y++)
                    {
                        if(cb[y][pomX] != 'x')
                        {
                            cb[y][pomX] = 'x';
                            count++;
                        }
                        pomX++;                    
                    }
                    
                    
                }
                else
                {
                    int pomY = q_y-q_x;
                    for(int x=0;x < cb_X;x++)
                    {
                        if(cb[pomY][x] != 'x')
                        {
                            cb[pomY][x] = 'x';
                            count++;
                        }
                        pomY++;                    
                    }
                    
                }
                    int pomX2 = q_x;
                    for(int y=q_y; y>=0, pomX2<=cb_X; y--)
                        {
                        
                        if(cb[y][pomX2] != 'x')
                        {
                            cb[y][pomX2] = 'x';
                            count++;
                        }                
                        pomX2++;       
                    }
                    int pomY2 = q_y;
                    for(int x=q_x; x>=0, pomY2<=cb_Y; x--)
                    {
                        
                        if(cb[pomY2][x] != 'x')
                        {
                            cb[pomY2][x] = 'x';
                            count++;
                        }                
                        pomY2++;       
                    }
                
            }
        
        }
    
    int celek = cb_X*cb_Y - count;
    printf("%d\n",celek);
    }

    return 0;
}