ABC008_D.cpp

#include <bits/stdc++.h>

using namespace std;

#define int long long
#define all(v) begin(v), end(v)
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
#define reps(i, s, n) for(int i = (int)(s); i < (int)(n); i++)
#define min(...) min({__VA_ARGS__})
#define max(...) max({__VA_ARGS__})

template<class T1, class T2> void chmin(T1 &a, T2 b){if(a>b)a=b;}
template<class T1, class T2> void chmax(T1 &a, T2 b){if(a<b)a=b;}

using pint = pair<int, int>;
using tint = tuple<int, int, int>;
using vint = vector<int>;

const int inf = 1LL << 55;
const int mod = 1e9 + 7;

map<tuple<int, int, int, int>, int> dp;

int W, H, N, X[33], Y[33];

int solve(int lx, int ly, int rx, int ry) {
  if(dp.count(tie(lx, ly, rx, ry))) return dp[tie(lx, ly, rx, ry)];

  int res = 0;
  rep(i, N) {
    if(lx <= X[i] && X[i] < rx && ly <= Y[i] && Y[i] < ry) {
      int lu = solve(lx, ly, X[i], Y[i]);
      int ld = solve(lx, Y[i]+1, X[i], ry);
      int ru = solve(X[i]+1, ly, rx, Y[i]);
      int rd = solve(X[i]+1, Y[i]+1, rx, ry);
      chmax(res, lu+ld+ru+rd+(rx-lx)+(ry-ly)-1);
    }
  }
  return dp[tie(lx, ly, rx, ry)] = res;
}

signed main()
{
  cin.tie(0);
  ios_base::sync_with_stdio(0);
  cout << fixed << setprecision(12);

  cin >> W >> H >> N;
  rep(i, N) cin >> X[i] >> Y[i], X[i]--, Y[i]--;
  cout << solve(0, 0, W, H) << endl;

  return 0;
}