#include<bits/stdc++.h>
using namespace std;
bool mp[20005][20005];
signed main(){
	int n,m,k,sum=0;
	cin>>n>>m>>k;
	for(int i=0,x,y;i<k;i++){
		cin>>x>>y;
		for(int h1=x,h2=x,l1=y,l2=y;h1>0||h2<=n||l1>0||l2<=m;h1--,h2++,l1--,l2++){
			if(h1>0&&l1>0)mp[h1][l1]=1;
			if(h2<=n&&l1>0)mp[h2][l1]=1;
			if(h1>0&&l2<=m)mp[h1][l2]=1;
			if(h2<=n&&l2<=m)mp[h2][l2]=1;
		}
		for(int i=1;i<=n;i++)mp[i][y]=1;
		for(int i=1;i<=m;i++)mp[x][i]=1;
	}
	for(int i=1;i<=n;i++)
		for(int j=1;j<=m;j++)
			sum+=!mp[i][j];
	cout<<sum;
	return 0;
}

10分