#include <stdio.h>
#include <stdlib.h>




int main()
{
    freopen("padure2.in","r",stdin);
    freopen("padure2.out","w",stdout);
    //FILE *f = fopen("padure2.in","r");
    //FILE *g = fopen("padure2.out","w");

    int n,m,i,j,k;
    scanf("%i%i",&n,&m);
    int**a,**c;
    a = (int**)malloc((n)*sizeof(int*));
    c = (int**)malloc((n)*sizeof(int*));

    for(i=0;i<=n;i++)
    {
        a[i] = (int*)calloc((m),sizeof(int));
        c[i] = (int*)calloc((m),sizeof(int));
    }
    scanf("%i",&k);
    while(k--)
    {
        scanf("%i%i",&i,&j);
        a[i-1][j-1] = 1;
    }

    for(i=1;i<=n;i++) c[i][0] = 1;
    for(i=1;i<=m;i++) c[0][i] = 1;

    for(j=1;j<n;j++)
    {
        for(i=1;i<m;i++)
        {
            if(a[i][j]==1)
            {
                c[i][j] = 0;
            }
            else
            {
                c[i][j] = c[i-1][j] + c[i][j-1];
            }
        }
    }

    printf("%i\n",c[n-1][m-1]);



    return 0;
}