#include<sstream>
#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<string>
#include<vector>
#include<set>
#include<map>
#include<queue>
#include<numeric>
#include<functional>
#include<algorithm>
using namespace std;
#define INF (1<<29)
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define all(v) v.begin(),v.end()
#define uniq(v) v.erase(unique(all(v)),v.end())
#define indexOf(v,x) (find(all(v),x)-v.begin())


int a[1000000],b[1000000];
int s[100],k[100];

int main(){
	int w,h,n,c=0;
	cin>>w>>h>>n;
	rep(i,n){
		cin>>s[i]>>k[i];
		s[i]--;k[i]--;
		a[s[i]]++;
		if(b[k[i]]++==0)c++;
	}
	long long ans=(long long)w*h-n;
	rep(i,w)if(a[i]==0){
		ans-=h-c;
	}
	cout<<ans<<endl;
	return 0;
}