#include<iostream>
#include<cassert>
using namespace std;
int H,W,N;
int a[1000],b[1000],c[1000],d[1000];
int x[2002],y[2002];
long dist[2002];
bool vis[2002];
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	cin>>H>>W>>N;
	for(int i=0;i<N;i++)
	{
		cin>>a[i]>>b[i]>>c[i]>>d[i];
		x[i]=a[i],y[i]=b[i];
		x[N+i]=c[i],y[N+i]=d[i];
	}
	x[2*N]=1,y[2*N]=1;
	x[2*N+1]=H,y[2*N+1]=W;
	for(int i=0;i<2*N+2;i++)dist[i]=1e18;
	dist[2*N]=0;
	while(true)
	{
		int mi=-1;
		for(int i=0;i<2*N+2;i++)if(!vis[i])
		{
			if(mi==-1||dist[mi]>dist[i])mi=i;
		}
		if(mi==-1)break;
		vis[mi]=true;
		for(int j=0;j<2*N+2;j++)
		{
			long d=dist[mi];
			d+=abs(x[mi]-x[j]);
			d+=abs(y[mi]-y[j]);
			if(dist[j]>d)
			{
				dist[j]=d;
			}
		}
		if(mi<N)
		{
			long d=dist[mi]+1;
			if(dist[mi+N]>d)
			{
				dist[mi+N]=d;
			}
		}
	}
	cout<<dist[2*N+1]<<endl;
}