#include<stdio.h>
#include <vector>
#include <list>
#include <map>
#include <set>
#include<unordered_set>
#include <queue>
#include <stack>
#include <algorithm>
#include <sstream>
#include <iostream>
#include <string>

using namespace std;

int main() {

	int W, H, N, S[105], K[105];
	cin >> W >> H >> N;
	for (int i = 0; i < N; i++) {
		cin >> S[i] >> K[i];
	}

	long long  ans = 0;
	unordered_set<int> s1, s2;

	bool flag = false;

	int nowNum = 1, cnt = 1, leftNum = 1;
	for (int i = 0; i < N; i++) {
		s2.insert(K[i]);
		if (nowNum != S[i]) {
			s1.insert(nowNum);
			for (int l = leftNum; l < 1000005; l++) {
				leftNum++;
				if (S[i] == leftNum) {
					nowNum = S[i];
					break;
				}
				
			}
			ans += (H - cnt);
			cnt = 1;
		}
		else {
			if(i!=0) cnt++;
		}
	}

	s1.insert(S[N-1]);
	ans += (H - cnt);

	ans += (W - s1.size())*s2.size();

	cout << ans << endl;

	return 0;
}