#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
#include <map>
#include <set>
#include <cmath>
#define ll long long
#define N 330000
using namespace std;
inline int read(){
	int x=0,f=1;char c=getchar();
	while(c<'0' or '9'<c) f=(c=='-'?-1:f),c=getchar(); 
	while('0'<=c and c<='9') x=x*10+c-'0',c=getchar();
	return x*f;
}
int w,h,n,ans;
int mx[N*4],flag[N*4];
struct node{
	int x,y;
	node(int _x=0,int _y=0):x(_x),y(_y){};
}p[N],a[N],b[N]; 
void change(int x,int l,int r,int v,int ql,int qr){
    if(ql<=l and r<=qr){
		mx[x]+=v;flag[x]+=v;
		return;
	}
    int mid=(l+r)>>1;
    if(ql<=mid) change(x<<1,l,mid,v,ql,qr);
    if(qr>mid) change(x<<1|1,mid+1,r,v,ql,qr);
    mx[x]=max(mx[x<<1],mx[x<<1|1])+flag[x];
}
bool cmp(node a,node b){
	return a.x<b.x or (a.x==b.x and a.y<b.y);
}
inline void work(){
    memset(mx,0,sizeof mx);
    memset(flag,0,sizeof flag);
    sort(p+1,p+n+1,cmp);
    int l=0,r=0;
    for(int i=1;i<n;i++){
        if(p[i].y<=h/2){
            int ed=i-1;
            while(l and a[l].y<p[i].y){
                change(1,1,n,a[l].y-p[i].y,a[l].x,ed);
				ed=a[l].x-1;l--; 
            }
            if(ed!=i-1) a[++l]=node(ed+1,p[i].y);
        }
        else{
            int ed=i-1;
            while(r and b[r].y>p[i].y){
                change(1,1,n,p[i].y-b[r].y,b[r].x,ed);
				ed=b[r].x-1;r--;
            }
            if(ed!=i-1) b[++r]=node(ed+1,p[i].y);
        }
        a[++l]=node(i,0);b[++r]=node(i,h);
        change(1,1,n,h-p[i].x,i,i);
        ans=max(ans,mx[1]+p[i+1].x);
    }
}
int main(){
//	freopen("a.in","r",stdin);
    w=read();h=read();n=read();
    for(int i=1;i<=n;i++) p[i].x=read(),p[i].y=read();
    p[++n]=node(0,0);p[++n]=node(w,h);
	work();
	swap(w,h);
    for(int i=1;i<=n;i++) swap(p[i].x,p[i].y);
    work();
    printf("%d",ans*2);
    return 0;
}