#include <bits/stdc++.h>

using namespace std;

long long n,a=0,b=0;
long long x[4007],y[4007];

int main()
{
    cin>>x>>y>>n;
    for(int i=1;i<n;i++)
       cin>>x[i]>>y[i];
    x[0] = y[0] = 0;
    x[n+1] = x + 1;
    y[n+1] = y + 1;
    n+=2;
    sort(x+1, x + n+1);
    sort(y+1, y + n+1);
    for(int i=2; i<n; i++){
        if(x[i]-x[i-1]>a)
         a=x[i+1]-x[i];
	if(y[i+1]-y[i]>b)
        b=y[i+1]-y[i];
    }
    cout<<(a-1)*(b-1);
    return 0;
}