2 5 10
2 2
1 1
1 4
2 1
1 2
1 5
2 4
2 5
1 3
2 3
 2 2 2
1 1
2 2
 3 3 9
1 1
1 2
1 3
2 1
2 2
2 3
3 1
3 2
3 3
 7 5 35
5 3
3 5
1 1
2 5
6 4
7 2
5 1
3 4
6 5
7 3
4 1
2 2
4 2
2 4
4 3
3 3
6 1
1 2
4 5
1 3
2 1
5 5
7 5
7 1
6 2
1 4
1 5
3 2
4 4
5 2
2 3
6 3
7 4
5 4
3 1
 1 5 4
1 1
1 2
1 4
1 5
 1 1 1
1 1
 5 7 21
4 4
4 5
5 5
5 6
5 7
5 1
5 2
4 2
3 2
3 1
3 7
3 6
2 6
1 6
1 7
1 1
1 2
1 3
1 4
2 4
3 4
 2 1 1
1 1
 2 2 4
2 1
1 1
1 2
2 2
 3000 3000 1
2222 738
 5 7 35
1 2
2 3
5 1
5 7
4 4
5 3
3 1
2 6
4 5
2 7
4 1
2 1
2 2
1 7
5 6
3 6
4 6
1 6
1 1
3 3
3 4
4 2
2 5
5 5
3 5
2 4
1 5
1 3
4 3
5 4
1 4
3 7
4 7
3 2
5 2
 5 4 1
4 1
 3 4 12
2 3
3 2
2 2
2 1
1 2
3 1
1 4
1 3
3 3
2 4
3 4
1 1
 3 3 3
1 1
2 2
3 3

8
 1
 6
 26
 4
 0
 20
 0
 2
 1
 28
 1
 9
 3

#include <bits/stdc++.h>
using namespace std;
const int a1[4] = {1, -1, 0, 0}, a2[4] = {0, 0, 1, -1};
struct ww {
  int x, y;
} g[3010 * 3010];
int i, j, k, n, m, K, x, y, l, r;
int ff[3010][3010], f[3010][3010], gg[3010][3010];
int main() {
  scanf("%d%d%d", &n, &m, &K);
  for (i = 1; i <= K; i++) {
    scanf("%d%d", &x, &y);
    f[x][y] = i;
  }
  l = 1, r = 0;
  for (i = 1; i <= m; i++)
    if (f[1][i])
      ff[1][i] = gg[1][i] = 1, g[++r] = (ww){1, i};
    else {
      ff[1][i] = 1;
      if (!(--l)) l = 3010 * 3010 - 1;
      g[l] = (ww){1, i};
    }
  for (; l != r;) {
    ww A = g[l];
    if ((++l) == 3010 * 3010) l = 1;
    for (i = 0; i <= 3; i++) {
      int x = A.x + a1[i], y = A.y + a2[i];
      if (x < 1 || x > n) continue;
      if (!y) y = m;
      if (y > m) y = 1;
      if (!ff[x][y]) {
        ff[x][y] = 1;
        if (f[x][y]) {
          gg[x][y] = gg[A.x][A.y] + 1;
          g[++r] = (ww){x, y};
        } else {
          gg[x][y] = gg[A.x][A.y];
          if (!(--l)) l = 3010 * 3010 - 1;
          g[l] = (ww){x, y};
        }
      }
    }
  }
  int an = 0;
  for (i = 1; i <= m; i++) an = max(an, K - gg[n][i]);
  printf("%d\n", an);
  return 0;
}
