#pragma GCC optimize("O3,unroll-loops")
#include<stdio.h>
#include<set>
#include<algorithm>
#include<vector>
int r,c,n;long long ans=1e10;
struct pt{int x,y;}p[333];
struct DQ{
int y[333*333],x[333*333],hd,tl;
void cl(){ hd=0;tl=1; }
DQ(){cl();}
void ins(int t,int va){
while(hd>=tl&&x[hd]<=va)--hd;
++hd;
x[hd]=va;
y[hd]=t;
}
void tim(int t){ while(hd>=tl&&y[tl]<t)++tl; }
int max(int t){ tim(t); return x[tl]; }
}L,R,LR;
int main(){
scanf("%d%d%d",&r,&c,&n);
for(int i=0;i<n;++i)scanf("%d%d",&p[i].x,&p[i].y);
std::sort(p,p+n,[](pt&a,pt&b){return a.x-b.x?a.x<b.x:a.y<b.y;});
std::sort(p,p+n,[](pt&a,pt&b){return a.y-b.y?a.y<b.y:a.x<b.x;});
n=std::unique(p,p+n,[](pt&a,pt&b){return a.x==b.x&&a.y==b.y;})-p;
auto CC=[&](int dw){
L.cl();R.cl();LR.cl();
int ban=0;
auto Chk=[&](int i){
if(i<1)i=1;
std::vector<int>e;
for(int j=0;j<n;++j)if((p[j].x<=i&&p[j].x+dw>=i))
e.push_back(p[j].y);
if(e.empty()){
ban=i;
return;
}
int gapmax=0;
for(int i=1;i<(int)e.size();++i)
gapmax=std::max(gapmax,e[i]-e[i-1]-1);
L.ins(i,e[0]-1);
R.ins(i,c-e.back());
LR.ins(i,gapmax);
if(ban<=i-r)
ans=std::min(ans,dw+0ll+std::max(L.max(i-r+1)+R.max(i-r+1),LR.max(i-r+1)));
};
std::vector<int>qwq;
for(int i=0;i<n;++i){
qwq.push_back(p[i].x-1); qwq.push_back(p[i].x);
qwq.push_back(p[i].x+dw+1);
qwq.push_back(p[i].x+dw);
}
std::sort(qwq.begin(),qwq.end());
qwq.resize(std::distance(qwq.begin(),std::unique(qwq.begin(),qwq.end())));
for(auto dw:qwq)Chk(dw);
};
auto CC_=[&](int dw){
L.cl();R.cl();LR.cl();
enum{ ADD,DEL,CHK };
static struct Event{ int type,x,id; }ev[9999];
int ban{},eo{};
for(int i=0;i<n;++i){
ev[eo++]=(Event){ADD,p[i].x,i};
ev[eo++]=(Event){DEL,p[i].x+dw+1,i};
ev[eo++]=(Event){CHK,p[i].x+dw,i};
ev[eo++]=(Event){CHK,p[i].x+dw+1,i};
ev[eo++]=(Event){CHK,p[i].x-1,i};
ev[eo++]=(Event){CHK,p[i].x,i};
}
std::sort(ev,ev+eo,[](Event&a,Event&b){
if(a.x!=b.x) return a.x<b.x;
return a.type<b.type;
});
struct {
std::multiset<int>s,gc;
int l,r,g;
void ins(int y){
if(!s.count(y)){
auto it=s.upper_bound(y);
if(it!=s.end()&&(it)!=s.begin()){
gc.erase(gc.find(*it-*prev(it)));
}
if(it!=s.end()) gc.insert(*it-y);
if((it)!=s.begin())gc.insert(y-*prev(it));
}
s.insert(y);
if(gc.size())
g=*gc.rbegin()-1;
if(s.size()){
l=*s.begin()-1;
r=c-*s.rbegin();
}
}
void rem(int y){
if(s.count(y)==1){
auto it=s.upper_bound(y),iy=s.lower_bound(y);
if(it!=s.end())gc.erase(gc.find(*it-y));
if(iy!=s.begin())gc.erase(gc.find(y-*prev(iy)));
if(it!=s.end()&&iy!=s.begin())gc.insert(*it-*prev(iy));
}
s.erase(s.find(y));
if(gc.size())
g=*gc.rbegin()-1;
if(s.size()){
l=*s.begin()-1;
r=c-*s.rbegin();
}
}
}gm;
for(int i1=0;i1<eo;++i1){
const auto&ee=ev[i1];
int x=ee.x;
if(ee.type==ADD){
gm.ins(p[ee.id].y);
}else if(ee.type==DEL){
gm.rem(p[ee.id].y);
}else{
L.ins(ee.x,gm.l);
R.ins(ee.x,gm.r);
LR.ins(ee.x,gm.g);
if(ban<=ee.x-r)
ans=std::min(ans,dw+0ll+std::max(L.max(x-r+1)+R.max(x-r+1),LR.max(x-r+1)));
}
if(gm.s.empty())ban=x;
}
};
std::sort(p,p+n,[](pt&a,pt&b){return a.x-b.x?a.x<b.x:a.y<b.y;});
std::vector<int>ud_cands={0},uu={p[0].x-1},dd={r-p[n-1].x};
for(int i=0;i<n;++i){
uu.push_back(p[i].x-1);
dd.push_back(r-p[i].x);
for(int j=i;j<n;++j)
if(p[j].x>p[i].x)
ud_cands.push_back(p[j].x-p[i].x-1);
}
for(auto u:uu)for(auto d:dd)ud_cands.push_back(u+d);
std::sort(ud_cands.begin(),ud_cands.end());
ud_cands.resize(std::distance(ud_cands.begin(),std::unique(ud_cands.begin(),ud_cands.end())));
std::sort(p,p+n,[](pt&a,pt&b){return a.y-b.y?a.y<b.y:a.x<b.x;});
for(auto ud:ud_cands)CC_(ud);
printf("%lld\n",ans);
return 0;
}
