#include<bits/stdc++.h>
using namespace std;
#define int long long
#define mp(a,b) make_pair(a,b)
const int N=309;
const int inf=2e9+10;
int r,c,n,ans;
struct node{
	int x,y;
	bool operator <(const node&A)const{
		return x<A.x;
	}
}p[N];
int L[N][N],R[N][N],Len[N][N];
multiset<int> ms;
multiset<int> ::iterator it,it1,it2;
void init(){
	for(int i=1;i<=n;i++){
		for(int j=i;j<=n;j++) ms.insert(p[j].y);
		L[i][n]=(*ms.begin())-1;
		it=ms.end(); it--; R[i][n]=c-(*it);
		it1=ms.begin(); it2=ms.begin(); it2++;
		for(;it2!=ms.end();it1++,it2++)
			Len[i][n]=max(Len[i][n],(*it2)-(*it1)-1);
		for(int j=n;j>i;j--){
			Len[i][j-1]=Len[i][j];
			it=ms.find(p[j].y);
			if(it!=ms.begin()){
				it--; it1=it;
				it++; it++; it2=it;
				if(it2!=ms.end())
					Len[i][j-1]=max(Len[i][j-1],(*it2)-(*it1)-1);
			}
			ms.erase(ms.find(p[j].y));
			it=ms.begin(); L[i][j-1]=(*it)-1;
			it=ms.end(); it--; R[i][j-1]=c-(*it);
			Len[i][j-1]=max(Len[i][j-1],L[i][j-1]+R[i][j-1]);
		}
		ms.clear();
	}
	return;
}
int solve(int len){//鎷撳睍len,闀垮害len+1
	list<pair<int,int> > ql,qr,qlen;
	ql.push_back(mp(inf,0)); qr.push_back(mp(inf,0)); qlen.push_back(mp(inf,0));
	int res=r+c;
	int pi=0,po=0;
	int ln=1,rn=0,nxt,now;
	p[n+1]=(node){inf,inf};
	while(pi<n||po<n){
		nxt=min(p[pi+1].x,p[po+1].x+len+1/*outside*/);
		while(pi<n&&p[pi+1].x==nxt){ rn++; pi++; }
		while(po<n&&p[po+1].x+len+1==nxt){ ln++; po++; }
		now=nxt; nxt=min(p[pi+1].x,p[po+1].x+len+1/*outside*/);
		if(pi==n&&po==n) break;
		nxt--;
		while(!ql.empty()&&ql.back().first<=L[ln][rn]) ql.pop_back();
		ql.push_back(mp(L[ln][rn],nxt));
		while(!qr.empty()&&qr.back().first<=R[ln][rn]) qr.pop_back();
		qr.push_back(mp(R[ln][rn],nxt));
		while(!qlen.empty()&&qlen.back().first<=Len[ln][rn]) qlen.pop_back();
		qlen.push_back(mp(Len[ln][rn],nxt));
		if(nxt>=r+p[1].x-1){
			while(ql.front().second<=nxt-r) ql.pop_front();
			while(qr.front().second<=nxt-r) qr.pop_front();
			while(qlen.front().second<=nxt-r) qlen.pop_front();
			res=min(res,max(ql.front().first+qr.front().first,qlen.front().first));
		}
	}
	return res;
}
vector<int> vx,vec;
signed main(){
	std::ios::sync_with_stdio(false);
	cin.tie(0);
	cin>>r>>c>>n; ans=r+c-2;
	for(int i=1;i<=n;i++){
		cin>>p[i].x>>p[i].y;
		vx.push_back(p[i].x);
	}
	sort(p+1,p+n+1);
	sort(vx.begin(),vx.end());
	vx.erase(unique(vx.begin(),vx.end()),vx.end());
	int l=vx[0]-1,rr=r-vx.back(); int mx=l+rr;
	for(int i=1;i<vx.size();i++) mx=max(mx,vx[i]-vx[i-1]-1);
	vec.push_back(mx);
	for(int i=0;i<vx.size();i++)
		for(int j=i+1;j<vx.size();j++)
			vec.push_back(vx[j]-vx[i]),vec.push_back(vx[j]-vx[i]+1),vec.push_back(r-vx[j]+vx[i]-1),vec.push_back(r-vx[j]+vx[i]);
	for(int i=0;i<vx.size();i++)
		vec.push_back(vx[i]-1),vec.push_back(r-vx[i]);
	sort(vec.begin(),vec.end());
	for(int i=0;i<vec.size();i++) if(vec[i]<mx) vec[i]=mx;
	vec.erase(unique(vec.begin(),vec.end()),vec.end());
	init();
	if(c==1000000000){
		cout<<Len[1][n]<<endl;
		return 0;
	}
	for(int len:vec)
//	for(int len=mx;len<=r;len++)
		ans=min(ans,solve(len)+len);
	cout<<ans;
	return 0;
}