#include <iostream>
#include <string>
#include <queue>
#include <stack>
#include <algorithm>
#include <list>
#include <vector>
#include <complex>
#include <utility>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <bitset>
#include <ctime>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <cassert>
#include <cstddef>
#include <iomanip>
#include <numeric>
#include <tuple>
#include <random>

#define REP(i,n) for(long (i)=0;(i)<(n);(i)++)
#define FOR(i,a,b) for(long (i)=(a);(i)<(b);(i)++)
#define RREP(i,a) for(long (i)=(a)-1;(i)>=0;(i)--)
#define FORR(i,a,b) for(long (i)=(a)-1;(i)>=(b);(i)--)
#define MOD 1000000007
#define PI acos(-1.0)
#define DEBUG(C) cout<<C<<endl;
#define PII pair<int,int>
#define PLL pair<long,long>
#define ALL(a) (a).begin(),(a).end()
#define SORT(a) sort((a).begin(),(a).end())
#define RSORT(a) sort((a).begin(),(a).end(),greater<int>())
#define MP(a,b) make_pair(a,b)

typedef long long LL;
typedef unsigned long long ULL;

using namespace std;

int main(void){
	long W,H,N; cin>>W>>H>>N;
	set<pair<long,long> > m;
	vector<long> S(N),K(N);
	REP(i,N){
		cin>>S[i]>>K[i];
		m.insert(MP(S[i],K[i]));
	}
	REP(i,N){
		FOR(j,1,W+1){
			m.insert(MP(j,K[i]));
		}
		REP(j,H){
			m.insert(MP(S[i],j));
		}
	}
	cout<<m.size()-N<<endl;
	//for(auto i:m) cout<<i.first<<" "<<i.second<<endl;
}