#include <stdio.h>
#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
using mint = modint998244353;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000001
#define Inf64 1000000000000000001

int main(){
	
	ios::sync_with_stdio(false);
	std::cin.tie(nullptr);
	
	long long H,W,N;
	cin>>H>>W>>N;
	
	vector<long long> a(N),b(N),c(N),d(N);
	rep(i,N){
		cin>>a[i]>>b[i]>>c[i]>>d[i];
	}
	a.push_back(1);
	b.push_back(1);
	c.push_back(1);
	d.push_back(1);
	a.push_back(H);
	b.push_back(W);
	c.push_back(H);
	d.push_back(W);
	vector<long long> dis(N+2,Inf64);
	dis[N] = 0;
	vector<bool> f(N+2,false);
	while(true){
		int ii = -1;
		rep(i,N+2){
			if(f[i])continue;
			if(ii==-1)ii = i;
			else if(dis[ii] > dis[i])ii = i;
		}
		if(ii==-1)break;
		f[ii] = true;
		rep(i,N+2){
			dis[i] = min(dis[i],dis[ii] + abs(d[ii] - b[i]) + abs(c[ii] - a[i]) + 1);
		}
	}
	cout<<dis[N+1] - 1<<endl;
	
	return 0;
}