#pragma comment(linker, "/STACK:60777216")  

#include <cassert>
#include<iostream>
#include<algorithm>
#include<cstdio>
#include<complex>
#include<vector>
#include<set>
#include<map>
#include<cmath>
#include<queue>
#include<string>
#include<cstdlib>
#include<memory.h>
#include<ctime>
#include<bitset>
#include<fstream>
#include<queue>

using namespace std;


typedef long double ld;

typedef long long ll;
typedef pair<int,int>	pii;
typedef pair<ld,ld>	pdd;
typedef vector<int> vi;
typedef vector<ld> vd;
typedef pair<ll,ll> pl;

#define FOR(i,a,b)		for(int i=(a);i<(b);i++)
#define REP(i,n)		FOR(i,0,n)
#define SORT(v)			sort((v).begin(),(v).end())
#define UN(v)			SORT(v),(v).erase(unique((v).begin(),(v).end()),(v).end())
#define CL(a,b)			memset(a,b,sizeof a)
#define pb				push_back

int n,m,k;
int x[111111];
int y[111111];
vi xx,yy;

const int st = 131072;
set<int>  v[2*st];

void init(int x,int y){
	x+=st;
	while(x){
		v[x].insert(y);
		x>>=1;
	}
}
bool hasVal(int pos, int y1,int y2){
	set<int>::iterator it=v[pos].lower_bound(y1);
	return it!=v[pos].end() && *it<=y2;
}

bool good(int i, int d){
	int fromx = xx[x[i]]-d;
	int tox = fromx+d+d;
	fromx=lower_bound(xx.begin(),xx.end(),fromx)-xx.begin();
	tox=lower_bound(xx.begin(),xx.end(),tox+1)-xx.begin()-1;
	fromx+=st;
	tox+=st;
	while(fromx<=tox){
		if(hasVal(fromx, y[i] - d, y[i]+d)) return true;
		if(hasVal(tox,y[i]-d,y[i]+d)) return true;
		fromx=(fromx+1)>>1;
		tox=(tox-1)>>1;
	}
	return false;
}

int main(){	
#ifdef LocalHost
	freopen("input.txt","r",stdin);
	//freopen("output.txt","w",stdout);
#endif
#ifndef LocalHost
	freopen("robot.in","r",stdin);
	freopen("robot.out","w",stdout);
#endif

	cin>>n>>m>>k;
	REP(i,k)scanf("%d %d",x+i,y+i),xx.pb(x[i]),yy.pb(y[i]);
	UN(xx);UN(yy);
	REP(i,k){
		x[i]=lower_bound(xx.begin(),xx.end(),x[i])-xx.begin();
	//	y[i]=lower_bound(yy.begin(),yy.end(),y[i])-yy.begin();
	}
	int res = 1e9+13;
	REP(i,k){
		int from = 1;
		int to = res - 1;
		while(from<=to){
			int s = (from+to)>>1;
			if(good(i,s)) res=s,to=s-1;
			else from=s+1;
		}
		init(x[i],y[i]);
	}
	cout<<res<<endl;
	
#ifdef LocalHost
	printf("TIME: %.3lf\n",ld(clock())/CLOCKS_PER_SEC);
#endif
	return 0;
}