//from Kuugo
#include<bits/stdc++.h>
using namespace std;
#define N 1111116
 
int w,h,n,l[N],r[N],f[N],g[N],ans;
 
struct node{int x,y;}a[N];
vector<node> ql,qr;
bool cmp(node a,node b){return a.y<b.y;}
 
void build(int t,int x,int y){
	l[t]=x;r[t]=y;f[t]=0;g[t]=0;
	if (x==y){f[t]=w-a[x].y;return;}
	build(2*t,x,(x+y)/2);
	build(2*t+1,(x+y)/2+1,y);
	f[t]=max(f[2*t],f[2*t+1]);
}
 
void modify(int t,int x,int y,int z){
	if (x<=l[t]&&y>=r[t]) {f[t]+=z;g[t]+=z;return;};
	if (x<=r[2*t]) modify(2*t,x,y,z);
	if (y>=l[2*t+1]) modify(2*t+1,x,y,z);
	f[t]=max(f[2*t],f[2*t+1])+g[t];
}
 
void solve(){
	sort(a+1,a+n+1,cmp);
	build(1,0,n);
	ql.clear();ql.push_back((node){0,-1});ql.push_back((node){0,0});
	qr.clear();qr.push_back((node){w,-1});qr.push_back((node){w,0});
	for (int i=1;i<=n;i++){
		ans=max(ans,(f[1]+a[i].y)*2);
		if (a[i].x<=w/2){
			for (int j=ql.size()-1;j&&ql[j].x<=a[i].x;ql.pop_back(),j--)
				modify(1,ql[j-1].y+1,ql[j].y,ql[j].x-a[i].x);
			ql.push_back((node){a[i].x,i-1});
		}
		else {
			for (int j=qr.size()-1;j&&qr[j].x>=a[i].x;qr.pop_back(),j--)
				modify(1,qr[j-1].y+1,qr[j].y,a[i].x-qr[j].x);
			qr.push_back((node){a[i].x,i-1});
		}
		ql.push_back((node){0,i});
		qr.push_back((node){w,i});
	}
	ans=max(ans,(f[1]+h)*2);
}
 
int read(){
	int x=0,f=1;char ch=getchar();
	for (;!isdigit(ch);ch=getchar()) if (ch=='-') f=-f;
	for (;isdigit(ch);ch=getchar()) x=x*10+ch-'0';
	return x*f;
}
 
int main(){
	w=read();h=read();n=read();
	for (int i=1;i<=n;i++) a[i].x=read(),a[i].y=read();
	solve();
	for (int i=1;i<=n;i++) swap(a[i].x,a[i].y);
	swap(h,w);solve();
	printf("%d\n",ans);
	return 0;
}