#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>>no(h);
  vector<vector<bool>>a(h,vector<bool>(w,false));
  int n;
  cin>>n;
  rep(i,n){
    int x,y;
    cin>>x>>y;
    x--,y--;
    a[x][y]=1;
  }
  rep(i,h){
    rep(j,w)if(a[i][j])no[i].push_back(j);
    no[i].push_back(w);
  }
  rep(j,w){
    vector<S>dat(w,{1,0});
    lazy_segtree<S,op,e,int,mapping,composition,id>seg(dat);
    vector<int>b(h);
    rep(i,h){
      b[i]=*lower_bound(all(no[i]),j)-j;
    }
    seg.apply(0,w,-1);
    rep(i,h){
      ans+=i*b[i]-seg.prod(0,b[i]).sum;
      seg.apply(b[i],w,i);
    }
    continue;
    stack<pair<int,int>>st;
    st.push({-1,-1});
    vector<pair<int,int>>lftrht(h);
    rep(i,h){
      while(st.top().second>=b[i]){
        assert(!st.empty());
        st.pop();
      }
      lftrht[i].first=st.top().first+1;
      ans+=(i-st.top().first)*b[i];
      st.push({i,b[i]});
    }
    while(!st.empty())st.pop();
    st.push({h,-1});
    for(int i=h-1;i>=0;i--){
      while(st.top().second>=b[i]){
        assert(!st.empty());
        st.pop();
      }
      lftrht[i].second=st.top().first-1;
      ans+=(st.top().first-i)*b[i];
      st.push({i,b[i]});
    }
  }
  cout<<ans<<endl;
}