#include <iostream>
#include <vector>
#include <map>
#include <limits.h>
#include <algorithm>
using namespace std;

int main() {
  //std::cout << "Hello World!\n";
  
  int n, m, k;
  cin >> n >> m >> k;
  map<int, vector<int>> xs;
  map<int, vector<int>> ys;

  int minx = INT_MAX;
  int miny = INT_MAX;
  int maxx = 0;
  int maxy = 0;
  

  for (int i = 0; i < k; i++) {
    int x, y;
    cin >> x >> y;

    if (xs.find(x) == xs.end()) {
      xs[x] = {y};
    } else {
      xs[x].push_back(y);
    }

    if (ys.find(y) == ys.end()) {
      ys[y] = {x};
    } else {
      ys[y].push_back(x);
    }

    if (x!= 1 && x < minx) {
      minx = x;
    }

    if (x!= n && x > maxx) {
      maxx = x;
    }

    if (y!= 1 && y < miny) {
      miny = y;
    }

    if (y!= m && y > maxy) {
      maxy = y;
    }
  }

  int maxside;
  if (k == 0) {
    maxside = min(n, m);
  } else {
    maxside = min({n - maxx, m - maxy, minx - 1, miny - 1});
  }

  map<int, vector<int>> ::iterator itx;
  for (itx = xs.begin(); itx != xs.end(); itx++)
  {
    vector<int> vals = itx->second;
    sort(vals.begin(), vals.end());
    for (int j = 0; j < vals.size() - 1; j++) {
      if (vals[j+1] - vals[j] - 1 != 0 && vals[j+1] - vals[j] - 1 < maxside) {
        maxside = vals[j+1] - vals[j] - 1;
      }
    }
  }

  map<int, vector<int>> ::iterator ity;
  for (ity = ys.begin(); ity != ys.end(); ity++)
  {
    vector<int> vals = ity->second;
    sort(vals.begin(), vals.end());
    for (int j = 0; j < vals.size() - 1; j++) {
      if (vals[j+1] - vals[j] - 1 != 0 && vals[j+1] - vals[j] - 1 < maxside) {
        maxside = vals[j+1] - vals[j] - 1;
      }
    }
  }

  cout << maxside << "\n";
  
}