#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cmath>
#include<stack>
#include<queue>
#include<cstring>
#include<vector>
#include<map>
using namespace std;
typedef long long ll;
#define N 301002
struct quji{int l,r,mid,mx,laz;}c[N<<2];
struct node{int x,y;}a[N];
struct qj{int st,va;}s1[N],s2[N];
int w,h,n,ans,tot1,tot2;
bool cmp(node n1,node n2){return n1.y<n2.y;}
void bt(int ind,int l,int r)
{
	c[ind].l=l;c[ind].r=r;c[ind].mid=(l+r)>>1;c[ind].laz=0;
	if(l==r){c[ind].mx=-a[l].y;return;}
	bt(ind<<1,l,c[ind].mid);bt(ind<<1|1,c[ind].mid+1,r);
	c[ind].mx=max(c[ind<<1].mx,c[ind<<1|1].mx);
}
void pushdown(int ind)
{
	c[ind<<1].laz+=c[ind].laz;
	c[ind<<1].mx+=c[ind].laz;
	c[ind<<1|1].laz+=c[ind].laz;
	c[ind<<1|1].mx+=c[ind].laz;
	c[ind].laz=0;
}
void chng(int ind,int l,int r,int x)
{if(l>r)return;if(l==0)return;
	if(l<=c[ind].l&&c[ind].r<=r)
	{
		c[ind].laz+=x;c[ind].mx+=x;
		return;
	}
	pushdown(ind);
	if(l<=c[ind].mid)chng(ind<<1,l,r,x);
	if(r>c[ind].mid)chng(ind<<1|1,l,r,x);
	c[ind].mx=max(c[ind<<1].mx,c[ind<<1|1].mx);
}
int ask(int ind,int l,int r)
{if(l>r)return -1e9;
	if(l<=c[ind].l&&c[ind].r<=r)return c[ind].mx;
	int ret=-1e9;pushdown(ind);
	if(l<=c[ind].mid)ret=max(ret,ask(ind<<1,l,r));
	if(r>c[ind].mid)ret=max(ret,ask(ind<<1|1,l,r));
	return ret;
}
void solve()
{
	sort(a+1,a+1+n,cmp);
	int ls=0,rs=w;
	for(int i=n;i;i--)
	{
		ans=max(ans,h-a[i].y+rs-ls);
		if(a[i].x<=w/2)ls=max(ls,a[i].x);
		else rs=min(rs,a[i].x);
	}ans=max(ans,h+rs-ls);
	tot1=tot2=0;
	bt(1,1,n);
	ls=0,rs=w;
	bool f1=false,f2=false;
	for(int i=1;i<=n;i++)
	{
		/*ls=0,rs=w;
		for(int j=i-1;j;j--)
		{
			ans=max(ans,a[i].y-a[j].y+rs-ls);
			if(a[j].x<=w/2)ls=max(ls,a[j].x);
			else rs=min(rs,a[j].x);
		}
		ans=max(ans,a[i].y+rs-ls);*/
		ans=max(ans,rs-ls+a[i].y);
		int tv=ask(1,1,i-1);
		ans=max(ans,tv+a[i].y);
		chng(1,i,i,w);
		if(a[i].x<=w/2)
		{
			ls=max(ls,a[i].x);
			int la=i-1;
			while(tot1&&a[i].x>s1[tot1].va)
			{
				chng(1,s1[tot1].st,la,s1[tot1].va-a[i].x);
				la=s1[tot1].st-1;tot1--;
			}
			if(la<i-1)s1[++tot1].st=la+1,s1[tot1].va=a[i].x;
		}
		else
		{
			rs=min(rs,a[i].x);
			int la=i-1;
			while(tot2&&a[i].x<s2[tot2].va)
			{
				chng(1,s2[tot2].st,la,a[i].x-s2[tot2].va);
				la=s2[tot2].st-1;tot2--;
			}
			if(la<i-1)s2[++tot2].st=la+1,s2[tot2].va=a[i].x;
		}
		s1[++tot1].st=i,s1[tot1].va=0;
		s2[++tot2].st=i,s2[tot2].va=w;
	}
	//puts("fin");
	//printf("%d\n",ans);
}
int main()
{
	scanf("%d%d%d",&w,&h,&n);
	if(!n){printf("%d\n",2*(w+h));return 0;}
	for(int i=1;i<=n;i++)scanf("%d%d",&a[i].x,&a[i].y);
	solve();
	for(int i=1;i<=n;i++)swap(a[i].x,a[i].y);
	swap(w,h);solve();
	printf("%d\n",ans*2);return 0;
}
/*
10 10 4
1 6
4 1
6 9
9 4
*/