#include<bits/stdc++.h>
using namespace std;

int n,m,k,ans,x,y;
bool row[20005],col[20005],a[40005],b[40005];

int main(){
	ios_base::sync_with_stdio(0),cin.tie(0),cout.tie(0);
	
	cin >> n >> m >> k;
	while(k--){
		cin >> x >> y;
		
		row[x] = col[y] = a[x + y] = b[m + x - y] = 1;
	}
	
	for(int i = 1; i <= n; i++){
		if(row[i])
			continue;
		for(int j = 1; j <= m; j++){
			if(!col[j] && !a[i+j] && !b[m+i-j])
				ans++;
		}
	}
	
	cout << ans;
	
	return 0;
}