#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)
#define esper(...) 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_popcountll(x)
#define fin(x) return cout<<x<<'\n',static_cast<void>(0)
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);
  cout<<fixed<<setprecision(16);
  #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
}
template<typename T,bool MIN=true>
vector<int>cartesian_tree(vector<T>&a){
  int n=a.size();
  if constexpr(!MIN){
    rep(i,n)a[i]*=-1;
  }
  vector<int>ret(n,-1);
  stack<int>st;
  rep(i,n){
    int ls=-1;
    while(!st.empty()){
      int x=st.top();
      if(a[x]>=a[i]){
        ls=x;
        st.pop();
      }
      else break;
    }
    if(ls!=-1)ret[ls]=i;
    if(!st.empty())ret[i]=st.top();
    st.push(i);
  }
  return ret;
}
void SOLVE(){
  int h,w,n;
  cin>>h>>w>>n;
  vector<string>s(h,string(w,'.'));
  rep(i,n){
    int a,b;
    cin>>a>>b;
    a--,b--;
    s[a][b]='#';
  }
  ll ans=0;
  vector<int>dp(w,0);
  for(int i=h-1;i>=0;i--){
    rep(j,w){
      if(s[i][j]=='#')dp[j]=0;
      else dp[j]++;
    }
    auto c=cartesian_tree(dp);
    vector<int>left(w,-1),right(w,-1);
    int root=-1;
    rep(j,w){
      if(c[j]==-1)root=j;
      else (j<c[j]?left:right)[c[j]]=j;
    }
    auto dfs=[&](auto self,int x,int l,int r)->void {
      ans+=ll(dp[x])*(x-l+1)*(r-(x+1)+1);
      if(left[x]!=-1)self(self,left[x],l,x);
      if(right[x]!=-1)self(self,right[x],x+1,r);
    };
    dfs(dfs,root,0,w);
  }
  cout<<ans<<endl;
}