#include<bits/stdc++.h>
#define rep(i,a,b) for(int i=(a);i<=(b);i++)
#define per(i,a,b) for(int i=(a);i>=(b);i--)
#define fi first
#define se second
#define eb emplace_back
#define popc __builtin_popcount
#define clz __builtin_clz
#define ctz __builtin_ctz
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<pii> vp;
typedef long double ld;
typedef unsigned long long ull;

int read() {
  int x=0,w=1; char c=getchar(); 
  while(!isdigit(c)) {if(c=='-') w=-1; c=getchar();}
  while(isdigit(c)) {x=x*10+(c-'0'); c=getchar();}
  return x*w;
}

const int N=309,inf=1e12;
int R,C,n,f[N][N],g[N][N],h[N][N],k[N*N*2],tot,cnt,ans,sum;
int b[N*2],af[N*2],ag[N*2],ah[N*2];
struct node {int x,y;} a[N];
multiset<int>sh;
set<int>sp;

bool cmp(const node &a,const node &b) {
  return a.x==b.x?a.y<b.y:a.x<b.x;
}

signed main() {
  R=read(), C=read(), n=read(), ans=inf;
  rep(i,1,n) a[i].x=read(), a[i].y=read();
  sort(a+1,a+n+1,cmp); k[++tot]=0; k[++tot]=R-1;
  rep(i,1,n) rep(j,1,n) if(a[i].x-a[j].x>0) k[++tot]=a[i].x-a[j].x-1;
  rep(i,1,n) rep(j,1,n) if(R-a[i].x+a[j].x>0) k[++tot]=R-a[i].x+a[j].x-1;
  sort(k+1,k+tot+1); tot=unique(k+1,k+tot+1)-k-1;
  rep(l,1,n) {
    sh.clear(), sp.clear(); int sf=inf, sg=inf;
    rep(r,l,n) {
      sf=min(sf,a[r].y-1), sg=min(sg,C-a[r].y);
      auto it=sp.lower_bound(a[r].y);
      if(it!=sp.begin()&&it!=sp.end()) {
        auto tmp=it; int xl=*--tmp, xr=*it;
        sh.erase(sh.find(xr-xl-1));
      }
      if(it!=sp.begin()) {
        auto tmp=it; int xl=*--tmp;
        sh.insert(a[r].y-xl-1);
      }
      if(it!=sp.end()) {
        int xr=*it;
        sh.insert(xr-a[r].y-1);
      }
      sp.insert(a[r].y);
      if(sh.size()) h[l][r]=*sh.rbegin();
      f[l][r]=sf, g[l][r]=sg;
    }
  }
  rep(l,1,n+1) rep(r,1,n+1) if(l>r||l>n||r>n)
    f[l][r]=g[l][r]=h[l][r]=inf;
  rep(t,1,tot) {
    rep(i,1,n) b[i]=a[i].x, b[i+n]=a[i].x+k[t]+1;
    inplace_merge(b+1,b+n+1,b+2*n+1);
    cnt=unique(b+1,b+2*n+1)-b-1;
    int l=1, r=1, tick=0;
    rep(i,1,cnt) {
      while(l<=n&&a[l].x<b[i]-k[t]) ++l;
      while(r<n&&a[r+1].x<=b[i]) ++r;
      if(i==1||f[l][r]!=af[tick]||g[l][r]!=ag[tick]||h[l][r]!=ah[tick])
        ++tick, af[tick]=f[l][r], ag[tick]=g[l][r], ah[tick]=h[l][r], b[tick]=b[i];
    }
    cnt=tick;
    static int qf[N*2],lf,rf; lf=1, rf=0;
    static int qg[N*2],lg,rg; lg=1, rg=0;
    static int qh[N*2],lh,rh; lh=1, rh=0;
    int res=inf; sum+=cnt;
    rep(i,1,cnt-1) {
      while(lf<=rf&&af[qf[rf]]<=af[i]) --rf;
      while(lg<=rg&&ag[qg[rg]]<=ag[i]) --rg;
      while(lh<=rh&&ah[qh[rh]]<=ah[i]) --rh;
      qf[++rf]=qg[++rg]=qh[++rh]=i;
      while(lf<=rf&&b[i+1]-b[qf[lf]+1]>=R) ++lf;
      while(lg<=rg&&b[i+1]-b[qg[lg]+1]>=R) ++lg;
      while(lh<=rh&&b[i+1]-b[qh[lh]+1]>=R) ++lh;
      int mf=af[qf[lf]], mg=ag[qg[lg]], mh=ah[qh[lh]];
      if(b[i+1]-b[1]>=R&&mf<inf&&mg<inf&&mh<inf)
        res=min(res,max(mf+mg,mh));
    }
    ans=min(ans,res+k[t]);
  }
  printf("%lld\n",ans);
  return 0;
}