#include <bits/stdc++.h>
#include <atcoder/segtree>
using namespace atcoder;
using namespace std;
using ll = long long;
struct Edge {
	int to;
	ll cost;
};
using Graph = vector<vector<Edge>>;
ll INF = (1LL << 60);
void DJK(int s, vector<ll>& dist, Graph& G) {
	dist[s] = 0;
	priority_queue<pair<ll, int>, vector<pair<ll,int>>, greater<pair<ll, int>>> pq;
	int N = G.size();
	for (int v = 0;v < N;v++) pq.emplace(dist[v], v);
	while (!pq.empty()) {
		int v = pq.top().second;ll dis = pq.top().first;pq.pop();
		if (dist[v] < dis) continue;
		for (auto nv : G[v]) {
			ll cost = nv.cost + dis;
			if (cost < dist[nv.to]) {
				dist[nv.to] = cost;
				pq.emplace(dist[nv.to], nv.to);
			}
		}
	}
}
int main() {
	ll H, W;int N;cin >> H >> W >> N;
	int K = (2 * N) + 2;
	vector<pair<ll, ll>> pos;
	pos.push_back({1, 1});
	pos.push_back({H, W});
	Graph G(K);
	for (int i = 0;i < N;i++) {
		ll a, b, c,d;cin >> a >> b >> c >> d;
		pos.push_back({a,b});
		int x = pos.size() - 1;
		pos.push_back({c, d});
		int y = pos.size() - 1;
		G[x].push_back({y, 1});
	}
	for (int i = 0;i < K;i++) for (int j = 0;j < K;j++) {
		if (i == j) continue;
		ll dist = abs(pos[i].first - pos[j].first) + abs(pos[i].second - pos[j].second);
		G[i].push_back({j, dist});
	}
	vector<ll> dist(K, INF);
	DJK(0, dist, G);
	cout << dist[1] << endl;
}