#include <bits/stdc++.h>
using namespace std;
#if __has_include(<atcoder/all>)
#include <atcoder/all>
using namespace atcoder;
template<int mod>istream &operator>>(istream &is,static_modint<mod> &a){long long b;is>>b;a=b;return is;}
istream &operator>>(istream &is,modint &a){long long b;cin>>b;a=b;return is;}
#endif
#ifdef LOCAL
#include "debug.h"
#else
#define debug(...) static_cast<void>(0)
#define debugg(...) static_cast<void>(0)
template<typename T1,typename T2>ostream &operator<<(ostream &os,const pair<T1,T2>&p){os<<p.first<<' '<<p.second;return os;}
#endif
using ll=long long;
using ull=unsigned long long;
using P=pair<ll,ll>;
template<typename T>using minque=priority_queue<T,vector<T>,greater<T>>;
template<typename T>bool chmax(T &a,const T &b){return (a<b?(a=b,true):false);}
template<typename T>bool chmin(T &a,const T &b){return (a>b?(a=b,true):false);}
template<typename T1,typename T2>istream &operator>>(istream &is,pair<T1,T2>&p){is>>p.first>>p.second;return is;}
template<typename T>istream &operator>>(istream &is,vector<T> &a){for(auto &i:a)is>>i;return is;}
template<typename T1,typename T2>void operator++(pair<T1,T2>&a,int n){a.first++,a.second++;}
template<typename T1,typename T2>void operator--(pair<T1,T2>&a,int n){a.first--,a.second--;}
template<typename T>void operator++(vector<T>&a,int n){for(auto &i:a)i++;}
template<typename T>void operator--(vector<T>&a,int n){for(auto &i:a)i--;}
#define reps(i,a,n) for(int i=(a);i<(n);i++)
#define rep(i,n) reps(i,0,n)
#define all(x) x.begin(),x.end()
#define pcnt(x) __builtin_popcount(x)
ll myceil(ll a,ll b){return (a+b-1)/b;}
struct S{
  int sz;
  int sum;
};
S op(S x,S y){return {x.sz+y.sz,x.sum+y.sum};}
S e(){return {0,0};}
S mapping(int f,S x){
  if(f!=-10)x.sum=f*x.sz;
  return x;
}
int composition(int f,int g){
  if(f!=-10)return f;
  return g;
}
int id(){return -10;}
int read_int() {
    int ret = 0;
    char ch = getchar_unlocked();
    while (isspace(ch)) { ch = getchar_unlocked(); }
    for (; isdigit(ch); ch = getchar_unlocked())
        ret = (ret * 10) + (ch - '0');
    ungetc(ch, stdin);
    return ret;
}
short a[3000][3000];
int main(){
  int h,w;
  h=read_int(),w=read_int();
  ll ans=0;
  int n;
  n=read_int();
  int x,y;
  rep(i,h)rep(j,w)a[i][j]=-1;
  rep(i,n){
    x=read_int(),y=read_int();
    a[x-1][y-1]=0;
  }
  for(int i=h-1;i>=0;--i)rep(j,w)if(a[i][j]==-1){
    if(i==h-1)a[i][j]=1;
    else a[i][j]=a[i+1][j]+1;
  }
  vector<S>dat(4096,{1,0});
  lazy_segtree<S,op,e,int,mapping,composition,id>seg(dat);
  rep(i,h){
    seg.apply(0,h,-1);
    rep(j,w){
      ans+=j*a[i][j]-seg.prod(0,a[i][j]).sum;
      seg.apply(a[i][j],4096,j);
    }
  }
  cout<<ans<<endl;
}