#include <iostream>
#include <set>
using namespace std;
typedef long long int ll;
int main(){
	int w,h,n;	cin>>w>>h>>n;
	set<int> vars;
	set<int> vark;
	int s,k;
	for(int i=0;i<n;i++){
		cin>>s>>k;
		if(vars.find(s)==vars.end())	vars.insert(s);
		if(vark.find(k)==vark.end())	vark.insert(k);
	}
	ll ans=(w*h)-(w-(int)vars.size())*(h-(int)vark.size());
	ans-=n;
	cout<<ans<<endl;
	return 0;
}