#include <bits/stdc++.h>
using namespace std;
typedef signed long long ll;

#define _P(...) (void)printf(__VA_ARGS__)
#define FOR(x,to) for(x=0;x<(to);x++)
#define FORR(x,arr) for(auto& x:arr)
#define FORR2(x,y,arr) for(auto& [x,y]:arr)
#define ALL(a) (a.begin()),(a.end())
#define ZERO(a) memset(a,0,sizeof(a))
#define MINUS(a) memset(a,0xff,sizeof(a))
template<class T> bool chmax(T &a, const T &b) { if(a<b){a=b;return 1;}return 0;}
template<class T> bool chmin(T &a, const T &b) { if(a>b){a=b;return 1;}return 0;}
//-------------------------------------------------------

int H,W,N;
int U[3030][3030];

void solve() {
	int i,j,k,l,r,x,y; string s;
	
	MINUS(U);
	cin>>H>>W>>N;
	FOR(i,N) {
		cin>>y>>x;
		U[y-1][x-1]=y-1;
	}
	FOR(x,W) {
		for(y=1;y<H;y++) U[y][x]=max(U[y][x],U[y-1][x]);
	}
	ll ret=0;
	FOR(y,H) {
		vector<pair<int,int>> V={{0,-1}};
		int sum=0;
		FOR(x,W) {
			int h=y-U[y][x];
			sum+=h;
			while(V.back().first>h) {
				auto p=V.back();
				V.pop_back();
				if(V.back().first>h) {
					sum-=(p.first-V.back().first)*(x-p.second);
				}
				else {
					sum-=(p.first-h)*(x-p.second);
					V.push_back({h,p.second});
					break;
				}
			}
			V.push_back({h,x});
			ret+=sum;
		}
	}
	cout<<ret<<endl;
	
}


int main(int argc,char** argv){
	string s;int i;
	if(argc==1) ios::sync_with_stdio(false), cin.tie(0);
	FOR(i,argc-1) s+=argv[i+1],s+='\n'; FOR(i,s.size()) ungetc(s[s.size()-1-i],stdin);
	cout.tie(0); solve(); return 0;
}