#include <iostream>
#include <vector>
#include <queue>
using namespace std;

struct node {
  int x, y, size;
};

int n, m, k, x, y, size_l, size_r, ans = 0;
vector<pair<int, int>> obstructions;
vector<vector<bool>> obstructed_map;

queue<node> q;

bool check(int size) {
  vector<vector<int>> obstructed_prefix = vector<vector<int>>(n - size + 1, vector<int>(m - size + 1, 0));
  for (int i = 0; i < k; i++) {
    int x_1 = max(0, obstructions[i].first - size + 1);
    int y_1 = max(0, obstructions[i].second - size + 1);
    int x_2 = obstructions[i].first + 1;
    int y_2 = obstructions[i].second + 1;
    obstructed_prefix[x_1][y_1] += 1;
    if (x_2 < obstructed_prefix.size()) obstructed_prefix[x_2][y_1] -= 1;
    if (y_2 < obstructed_prefix[0].size()) obstructed_prefix[x_1][y_2] -= 1;
    if (x_2 < obstructed_prefix.size() && y_2 < obstructed_prefix[0].size()) obstructed_prefix[x_2][y_2] += 1;
  }
  
  for (int i = 0; i + size <= n; i++) {
    int total = 0;
    for (int j = 0; j + size <= m; j++) {
      total += obstructed_prefix[i][j];
      obstructed_prefix[i][j] = (i > 0) ? obstructed_prefix[i - 1][j] : 0;
      obstructed_prefix[i][j] += total;
    }
  }
  
	vector<vector<bool>> visited = vector<vector<bool>>(n - size + 1, vector<bool>(m - size + 1, false));
	for (int i = 0; i < visited.size(); i++) {
		for (int j = 0; j < visited[0].size(); j++) {
		  if (obstructed_prefix[i][j] == 0) {
			  q = queue<node>();
			  q.push({i, j, size});
			  while (!q.empty()) {
			    node cur = q.front();
			    q.pop();
			    
			    if (cur.x < 0 || cur.y < 0 || cur.x >= visited.size() || cur.y >= visited[0].size()) continue;
        	if (obstructed_prefix[cur.x][cur.y] != 0 || visited[cur.x][cur.y]) continue;
        	
        	visited[cur.x][cur.y] = true;
        	
        	q.push({cur.x - 1, cur.y, size});
        	q.push({cur.x + 1, cur.y, size});
          q.push({cur.x, cur.y - 1, size});
          q.push({cur.x, cur.y + 1, size});
		    }
		    
		    vector<vector<int>> visited_prefixes = vector<vector<int>>(n, vector<int>(m, 0));
		    for (int a = 0; a < visited.size(); a++) {
      		for (int b = 0; b < visited[0].size(); b++) {
      		  if (visited[a][b]) {
      		    int x_1 = a;
      		    int y_1 = b;
      		    int x_2 = a + size;
      		    int y_2 = b + size;
      		    
      		    visited_prefixes[x_1][y_1] = visited_prefixes[x_1][y_1] + 1;
      		    if (x_2 < n) visited_prefixes[x_2][y_1] = visited_prefixes[x_2][y_1] - 1;
      		    if (y_2 < m) visited_prefixes[x_1][y_2] = visited_prefixes[x_1][y_2] - 1;
      		    if (x_2 < n && y_2 < m) visited_prefixes[x_2][y_2] = visited_prefixes[x_2][y_2] + 1;
    		    }
      		}
        }
        
        
        for (int a = 0; a < n; a++) {
          int total = 0;
          for (int b = 0; b < m; b++) {
            total += visited_prefixes[a][b];
            visited_prefixes[a][b] = (a > 0) ? visited_prefixes[a - 1][b] : 0;
            visited_prefixes[a][b] += total;
            
            if (!obstructed_map[a][b] && visited_prefixes[a][b] == 0) {
              return false;
            }
          }
        }
        
        return true;
			}
		}
  }
  return true;
}

int main() {
	cin >> n >> m >> k;
	obstructions = vector<pair<int, int>>(k);
	obstructed_map = vector<vector<bool>>(n, vector<bool>(m, 0));
	for (int i = 0; i < k; i++) {
	  cin >> obstructions[i].first >> obstructions[i].second;
	  obstructions[i].first--; obstructions[i].second--;
	  
	  obstructed_map[obstructions[i].first][obstructions[i].second] = true;
	}

	size_l = 1;
	size_r = min(n, m);
	
	while (size_l < size_r) {
		int size_m = (size_l + size_r) / 2;
		
		if (check(size_m)) {
		  size_l = size_m + 1;
		  ans = max(ans, size_m);
		} else {
		  size_r = size_m;
		}
	}
	cout << ans << endl;
}