#include <bits/stdc++.h>
#pragma GCC optimize("Ofast","unroll-loops","omit-frame-pointer","inline")
#pragma GCC option("arch=native","tune=native","no-zero-upper")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx")
using namespace std;
unsigned char bits[15800000];
bool get_used (int ch) {
    int numb=14*ch;
    return bits[numb/8]&(1<<(numb%8));
}
int get_dist (int ch) {
    int ans=0;
    for (int numb=1;numb<=13;numb++) {
        ans+=(1<<(numb-1))*bool(bits[(ch*14+numb)/8]&(1<<((ch*14+numb)%8)));
    }
    return ans;
}
void set_used(int ch) {
    int numb=14*ch;
    bits[numb/8]|=(1<<numb%8);
}
void set_dist(int ch, int zn) {

    for (int numb=1;numb<=13;numb++) {
       if (zn&(1<<(numb-1))) bits[(ch*14+numb)/8]|=(1<<((ch*14+numb)%8));
    }
}
int main() {
    int a,b;
    cin>>a>>b;
   int k;
   cin>>k;
   queue <pair<short int, short int>> q;
   for (int i=0;i<k;i++) {
       int x,y; cin>>x>>y; x--; y--; set_used(3001*x+y);
       q.push({x,y});
   }
   short int max1=0;

   while (!q.empty()) {
       pair <short int, short int> c=q.front();
       q.pop();
     short int kek=get_dist(c.first*3001+c.second);
     max1=max(max1,kek);
       if (c.first>0 && get_used(c.first*3001+c.second-3001)==false) {
           set_used(c.first*3001+c.second-3001); set_dist(c.first*3001+c.second-3001,kek+1);
           q.push({c.first-1,c.second});
       }
       if (c.second>0 && get_used(c.first*3001+c.second-1)==false) {
           set_used(c.first*3001+c.second-1); set_dist(c.first*3001+c.second-1,kek+1);
           q.push({c.first,c.second-1});
       }
       if (c.first<a-1 && get_used(c.first*3001+c.second+3001)==false) {
           set_used(c.first*3001+c.second+3001); set_dist(c.first*3001+c.second+3001,kek+1);
           q.push({c.first+1,c.second});
       }
       if (c.second<b-1 && get_used(c.first*3001+c.second+1)==false) {
           set_used(c.first*3001+c.second+1); set_dist(c.first*3001+c.second+1,kek+1);
           q.push({c.first,c.second+1});
       }
   }
  cout<<max1;

    return 0;
}