#include<cstdio>
#include<algorithm>
#include<cstring>
#include<queue>
#include<vector>
#include<cmath>
using namespace std;
const int M=2e5+5;
const int N=1e3+5;
#define int long long
int Max(int x,int y){return x>y?x:y;}
int Min(int x,int y){return x>y?y:x;}
int Abs(int x){return x>0?x:-x;}
void write (int x) {
	if (x < 0) { 
		putchar ('-'); 
		x = (~x) + 1; 
	}
	if (x > 9) { 
		write (x / 10); 
	}
	putchar (x % 10 + '0');
} 
int read () {
	int f = 1, num = 0;
	char s = getchar (); 
	while (s > '9' || s < '0') { 
		if (s == '-') f = -1; 
		s = getchar (); 
	}
	while (s >= '0' && s <= '9') { 
		num = (num << 3) + (num << 1) + (s - '0');
		s = getchar (); 
	}
	return num *= f;
}
int Bit[M];
int H[M],W[M];
int n,m,K;
int ans;
vector<int> G[M];
int lowbit(int x){
	return x&(-x);
}
int Sum(int x){
	int res=0;
	for(int i=x;i>=1;i-=lowbit(i)){
		res+=Bit[i];
	}
	return res;
}
void update(int x,int y){
	for(int i=x;i<=n;i+=lowbit(i)){
		Bit[i]+=y;
	}
}
signed main(){
	n=read(),m=read(),K=read();
	for(int i=0;i<=n+1;i++) H[i]=m+1;
	for(int i=0;i<=m+1;i++) W[i]=n+1;
	for(int i=1;i<=K;i++){
		int x=read(),y=read();
		H[x]=Min(H[x],y);
		W[y]=Min(W[y],x);
	}
//	for(int i=1;i<=n;i++){
//		printf("%d\n",H[i]);
//	}
//	for(int i=1;i<=m;i++){
//		printf("%d\n",W[i]);
//	}
	for(int i=1;i<=n;i++){
		if(H[i]==1){
			for(int j=i+1;j<=n;j++) H[j]=1;
			break;
		}
		ans+=H[i]-1;
	}
	for(int i=1;i<=n;i++){
		G[H[i]].push_back(i);
	}
	for(int i=1;i<=m;i++){
		if(W[i]==1) break;
		ans+=Sum(W[i]-1);
		for(int j=0;j<G[i].size();j++){
			update(G[i][j],1);
		}
	}
	printf("%lld",ans);
	return 0;
}
// atcoder/abc186/F/main.cpp
// author: @___Johniel
// github: https://github.com/johniel/

#include <bits/stdc++.h>

#define each(i, c) for (auto& i : c)
#define unless(cond) if (!(cond))

using namespace std;

template<typename P, typename Q> ostream& operator << (ostream& os, pair<P, Q> p) { os << "(" << p.first << "," << p.second << ")"; return os; }
template<typename P, typename Q> istream& operator >> (istream& is, pair<P, Q>& p) { is >> p.first >> p.second; return is; }
template<typename T> ostream& operator << (ostream& os, vector<T> v) { os << "("; for (auto& i: v) os << i << ","; os << ")"; return os; }
template<typename T> istream& operator >> (istream& is, vector<T>& v) { for (auto& i: v) is >> i; return is; }
template<typename T> ostream& operator << (ostream& os, set<T> s) { os << "#{"; for (auto& i: s) os << i << ","; os << "}"; return os; }
template<typename K, typename V> ostream& operator << (ostream& os, map<K, V> m) { os << "{"; for (auto& i: m) os << i << ","; os << "}"; return os; }

template<typename T> inline T setmax(T& a, T b) { return a = std::max(a, b); }
template<typename T> inline T setmin(T& a, T b) { return a = std::min(a, b); }

using lli = long long int;
using ull = unsigned long long;
using point = complex<double>;
using str = string;
template<typename T> using vec = vector<T>;

constexpr array<int, 8> di({0, 1, -1, 0, 1, -1, 1, -1});
constexpr array<int, 8> dj({1, 0, 0, -1, 1, -1, -1, 1});
constexpr lli mod = 1e9 + 7;

template<typename T>
struct SegTree {
  int n;
  int origin_size;
  vector<T> v;
  using F = function<T(T, T)>;
  F fn;
  T e;
  SegTree(int n_, T e_, F fn_) {
    origin_size = n_;
    e = e_;
    fn = fn_;
    n = 1;
    while (n < n_) n *= 2;
    v.resize(2 * n - 1, e);
  }

  void update(size_t k, T a) {
    k += n - 1;
    v[k] = a;
    while (k > 0) {
      k = (k - 1) / 2;
      v[k] = fn(v[k * 2 + 1], v[k * 2 + 2]);
    }
    return ;
  }

  T operator [] (size_t idx) const {
    return v.at(idx + n - 1);
  }

  inline T operator () () const {
    return query(0, origin_size, 0, 0, n);
  }

  inline T operator () (size_t a) const {
    return query(a, a+1, 0, 0, n);
  }

  inline T operator () (size_t a, size_t b) const {
    return query(a, b, 0, 0, n);
  }

  inline T query(size_t a, size_t b) const {
    assert(a < b);
    assert(b <= origin_size);
    return query(a, b, 0, 0, n);
  }

  T query(size_t a, size_t b, size_t k, size_t l, size_t r) const {
    if (r <= a || b <= l) return e;
    if (a <= l && r <= b) return v.at(k);

    T vl = query(a, b, k * 2 + 1, l, (l + r) / 2);
    T vr = query(a, b, k * 2 + 2, (l + r) / 2, r);

    return fn(vl, vr);
  }
};

int main(int argc, char *argv[])
{
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.setf(ios_base::fixed);
  cout.precision(15);

  lli h, w;
  int m;
  while (cin >> h >> w >> m) {
    vec<pair<lli, lli>> v(m);
    cin >> v;
    each (i, v) --i.first, --i.second;

    const int N = 2 * 1e5 + 5;
    const lli inf = 1LL << 60;
    static lli mn[N];
    fill(mn, mn + N, h);
    each (i, v) {
      setmin(mn[i.second], i.first);
    }

    lli sum = 0;
    for (int j = 0; j < w; ++j) {
      if (mn[j] == 0) break;
      sum += mn[j];
    }

    static vec<int> u[N];
    fill(u, u + N, vec<int>());
    each (i, v) {
      u[i.first].push_back(i.second);
    }
    for (int i = 0; i < N; ++i) {
      sort(u[i].begin(), u[i].end());
    }
    if (u[0].size()) {
      for (int j = u[0].front(); j < w; ++j) {
        u[0].push_back(j);
      }
    }

    SegTree<int> segtree(N, 0, [] (int a , int b) { return a + b; });
    for (int i = 1; i < h; ++i) {
      if (u[i].size() && u[i].front() == 0) break;
      each (j, u[i - 1]) {
        segtree.update(j, 1);
      }
      sum += segtree.query(0, (u[i].empty() ? w : u[i].front()));
    }
    cout << sum << endl;
  }

  return 0;
}
