#include <bits/stdc++.h>
using namespace std;

using warp_zone=pair<pair<long long,long long>,pair<long long,long long>>;

long long dijkstra(const vector<warp_zone>& wz, int s, int t){
	int n=(int)wz.size();
	vector<long long> dist(n,LONG_LONG_MIN);
	dist[s]=-0LL;
	priority_queue<pair<long long, int>> Q;
	Q.push({dist[s],s});
	while(!Q.empty()){
		long long d;
		int v;
		tie(d,v)=Q.top();
		Q.pop();
		if(v==t){
			return ~dist[v];
		}
		if(d<dist[v]){
			continue;
		}
		for(int i=0;i<n;i++){
			long long cost=abs(wz[i].first.first-wz[v].second.first)+abs(wz[i].first.second-wz[v].second.second)+1;
			if(dist[v]-cost>dist[i]){
				dist[i]=dist[v]-cost;
				Q.push({dist[i],i});
			}
		}
	}
	return ~dist[t];
}


int main(){
	long long h,w;
	int n;
	cin >> h >> w >> n;
	vector<warp_zone> wz(n+2);
	wz[0]={{1,1},{1,1}};
	wz[n+1]={{h,w},{h,w}};
	for(int i=1;i<=n;i++){
		cin >> wz[i].first.first >> wz[i].first.second >> wz[i].second.first >> wz[i].second.second;
	}
	cout << dijkstra(wz,0,n+1) << endl;
	return EXIT_SUCCESS;
}