#include <bits/stdc++.h>
using ll = long long;
using std::cin;
using std::cout;
using std::endl;
std::mt19937 rnd(std::chrono::steady_clock::now().time_since_epoch().count());
template <class T>
inline bool chmax(T &a, T b)
{
  if (a < b)
  {
    a = b;
    return 1;
  }
  return 0;
}
template <class T>
inline bool chmin(T &a, T b)
{
  if (a > b)
  {
    a = b;
    return 1;
  }
  return 0;
}

const int inf = (int)1e9 + 7;
const long long INF = 1LL << 60;

void solve([[maybe_unused]] int CASE)
{
  int n, m, q;
  cin >> n >> m >> q;
  std::vector<std::pair<int, int>> vp(q);
  std::vector<std::vector<int>> mat(n, std::vector<int>(m));
  for (int i = 0; i < q; ++i)
  {
    cin >> vp[i].first >> vp[i].second;
    vp[i].first -= 1, vp[i].second -= 1;
    mat[vp[i].first][vp[i].second] = 1;
  }
  std::vector dp(4, std::vector(n, std::vector<int>(m)));
  if (mat[0][0])
    dp[3][0][0] = 1;

  for (int i = 0; i < n; ++i)
  {
    for (int j = 0; j < m; ++j)
    {
      if (i + 1 < n)
      {
        for (int S = 0; S < 4; ++S)
        {
          int nS = S;
          if (S >> 1 & 1)
            nS -= (1 << 1);
          chmax(dp[nS][i + 1][j], dp[S][i][j]);
          if (mat[i + 1][j] and nS == 0)
          {
            chmax(dp[3][i + 1][j], dp[S][i][j] + 1);
          }
        }
      }
      if (j + 1 < m)
      {
        for (int S = 0; S < 4; ++S)
        {
          int nS = S;
          if (S & 1)
            nS -= 1;
          chmax(dp[nS][i][j + 1], dp[S][i][j]);
          if (mat[i][j + 1] and nS == 0)
          {
            chmax(dp[3][i][j + 1], dp[S][i][j] + 1);
          }
        }
      }
    }
  }
  // for (int i = 0; i < n; ++i)
  // {
  //   for (int j = 0; j < m; ++j)
  //   {
  //     cout << dp[3][i][j] << " \n"[j + 1 == m];
  //   }
  // }
  int res = 0;
  for (int i = 0; i < 4; ++i)
    chmax(res, dp[i][n - 1][m - 1]);
  cout << res << endl;
}

int main()
{
  std::cin.tie(nullptr);
  std::ios::sync_with_stdio(false);

  int kkt = 1;
  // cin >> kkt;
  for (int jupi = 1; jupi <= kkt; jupi++)
    solve(jupi);
  return 0;
}