#include<stdio.h>
#include<algorithm>
#include<vector>
int r,c,n,ans=1e9,fup=1e9;
struct pt{int x,y;}p[333];
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),fup=std::min(fup,p[i].x-1);
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 up_plus_dw){
if(fup>up_plus_dw)return;
int up=fup,dw=up_plus_dw-fup;
int lef0=0,rig0=0,gapmax=0,ok=1;
auto Chk=[&](int i){
if(!ok)return;
if(i<1)i=1;if(i>r)i=r;
std::vector<int>e;
for(int j=0;j<n;++j)if((p[j].x-up<=i&&p[j].x+dw>=i))
e.push_back(p[j].y);
if(e.empty()){
ok=0;
return;
}
lef0=std::max(lef0,e[0]-1);
rig0=std::max(rig0,c-e.back());
for(int i=1;i<(int)e.size();++i)
gapmax=std::max(gapmax,e[i]-e[i-1]-1);
};
for(int i=0;ok&&i<n;++i){
Chk(p[i].x-up);
Chk(p[i].x-up-1);
Chk(p[i].x+dw+1);
Chk(p[i].x+dw);
}
if(ok){
ans=std::min(ans,up+dw+std::max(lef0+rig0,gapmax));
}
};
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("%d\n",ans);
return 0;
}
