#include<bits/stdc++.h>
using namespace std;
int x[1005],y[1005];
int a,b,c,d[20005],e[20005],sum,ans;
int main(){
	
	cin>>a>>b>>c;
	for(int i=1;i<=c;i++){
		cin>>x[i]>>y[i];
		e[x[i]]=1;
	}
	for(int i=1;i<=a;i++){
		if(e[i]==1){
			continue;
		}
		sum=b;
		for(int j=1;j<=c;j++){
			if(d[y[j]]!=i){
				sum--;
			}
			d[y[j]]=i;
			if(x[j]<i){
				if(y[j]+i-x[j]>=1&&y[j]+i-x[j]<=b){
					if(d[y[j]+i-x[j]]!=i){
						sum--;
					}
					d[y[j]-x[j]+i]=i;
				}
				if(y[j]-i+x[j]>=1&&y[j]-i+x[j]<=b){
					if(d[y[j]-i+x[j]]!=i){
						sum--;
					}
					d[y[j]-i+x[j]]=i;
				}
			}
			else{
				if(y[j]+(x[j]-i)>=1&&y[j]+(x[j]-i)<=b){
					if(d[y[j]+(x[j]-i)]!=i){
						sum--;
					}
					d[y[j]+(x[j]-i)]=i;
				}
				if(y[j]-(x[j]-i)>=1&&y[j]-(x[j]-i)<=b){
					if(d[y[j]-(x[j]-i)]!=i){
						sum--;
					}
					d[y[j]-x[j]+i]=i;
				}
			}
		}
		ans+=sum;
	}
	cout<<ans;
	return 0;
 }