#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#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;}
template<typename T,size_t n,size_t id=0>
auto vec(const int (&d)[n],const T &init=T()){
  if constexpr (id<n)return vector(d[id],vec<T,n,id+1>(d,init));
  else return init;
}
void SOLVE();
int main(){
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  #ifdef LOCAL
  clock_t start=clock();
  #endif
  int testcase=1;
  //cin>>testcase;
  for(int i=0;i<testcase;i++){
    SOLVE();
  }
  #ifdef LOCAL
  cerr<<"time:";
  cerr<<(clock()-start)/1000;
  cerr<<"ms\n";
  #endif
}
struct S{
  int sz;
  ll 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;}
void SOLVE(){
  int h,w;
  cin>>h>>w;
  ll ans=0;
  vector<vector<int>>a(h,vector<int>(w,-1));
  int n;
  cin>>n;
  rep(i,n){
    int x,y;
    cin>>x>>y;
    x--,y--;
    a[x][y]=0;
  }
  rep(i,h)for(int j=w-1;j>=0;j--)if(a[i][j]==-1){
    if(j==w-1)a[i][j]=1;
    else a[i][j]=a[i][j+1]+1;
  }
  vector<S>dat(w,{1,0});
  lazy_segtree<S,op,e,int,mapping,composition,id>seg(dat);
  rep(j,w){
    seg.apply(0,w,-1);
    rep(i,h){
      ans+=i*a[i][j]-seg.prod(0,a[i][j]).sum;
      seg.apply(a[i][j],w-j,i);
    }
  }
  cout<<ans<<endl;
}