#include <stdio.h>
#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
using mint = modint998244353;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000001
#define Inf64 4000000000000000001


int main(){
	int H,W,N;
	cin>>H>>W>>N;
	vector a(H,vector<int>(W));
	rep(i,N){
		int x,y;
		cin>>x>>y;
		x--,y--;
		a[x][y] = 1;
	}
	long long ans = 0;
	vector<int> c(W);
	rep(i,H){
		rep(j,W){
			if(a[i][j])c[j] = 0;
			else c[j]++;
		}
		
		stack<pair<long long,long long>> S;
		S.emplace(-1,-1);
		long long cur = 0;
		rep(j,W){
			while(S.top().second >= c[j]){
				auto p = S.top();
				S.pop();
				cur -= p.second * (p.first - S.top().first);
			}
			cur += c[j] * (j - S.top().first);
			S.emplace(j,c[j]);
			ans += cur;
		}
	}
	cout<<ans<<endl;
	
	return 0;
}