#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;

template<typename T> inline bool chmax(T &a, T b) { return ((a < b) ? (a = b, true) : (false)); }
template<typename T> inline bool chmin(T &a, T b) { return ((a > b) ? (a = b, true) : (false)); }
#define rep(i, n) for (int i = 0; i < (long long)(n); i++)
#define rep2(i, m ,n) for (int i = (m); i < (long long)(n); i++)
#define REP(i, n) for (long long i = 1; i < (long long)(n); i++)
typedef long long ll;
#define updiv(N,X) (N + X - 1) / X
#define l(n) n.begin(),n.end()
#define YesNo(Q) Q==1?cout<<"Yes":cout<<"No"
using P = pair<int, int>;
using mint = modint;
const int MOD = 998244353LL;
ll solve(vector<ll> w){
set<ll> st;
vector<pair<ll,ll>> v;
rep(i,w.size()){v.push_back(pair(w[i],i));}
sort(l(v));
st.insert(-1);
int n = w.size();
st.insert(n);
ll ans = 0;
rep(i,n){
  auto t = st.lower_bound(v[i].second);
  auto k = t;k--;
  ans += ((ll)(*t) - (ll)(*k) - 1) * v[i].first;
  st.insert(v[i].second);
}
return ans;
}
int main(){
  ll h,w,n;cin>>h>>w>>n;
  vector<vector<ll>> v(h,vector<ll>(w,0));
  rep(i,n){
  ll a,b;cin>>a>>b;a--;b--;
  v[a][b] = 1;
  }
  vector<vector<ll>> t(h,vector<ll>(w,0));
  rep(i,h){
    ll now = 0;
    rep(j,w){now++;if(v[i][w-j-1]==1){now = 0;}t[i][w-j-1] = now;}
  }
  ll ans = 0;
  rep(i,w){vector<ll> w(h);
  
    rep(j,h){w[j] = t[j][i];}
   // rep(j,h){cout << w[j] << " ";}cout<<endl;
    ans += solve(w);
    //cout << solve(w).val() << endl;
  }
  cout << ans << endl;
}