#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <queue>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using mint = modint998244353;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vvvll = vector<vvll>;
using vmi = vector<mint>;
using vvmi = vector<vmi>;
using vvvmi = vector<vvmi>;
#define all(a) (a).begin(), (a).end()
#define rep2(i, m, n) for (int i = (m); i < (n); ++i)
#define rep(i, n) rep2(i, 0, n)
#define drep2(i, m, n) for (int i = (m)-1; i >= (n); --i)
#define drep(i, n) drep2(i, n, 0)
using p = pair<int, int>;
int inf = 2e9+7;
int main(){

    int h, w, n; cin >> h >> w >> n;
    vector<p> vst(n), vg(n);
    rep(i, n){
        int a, b, c, d; cin >> a >> b >> c >> d;
        vst[i] = {a, b};
        vg[i] = {c, d};
    }
    vvi dist(2*n+2, vi(2*n+2, inf));
    p goal = {h, w};
    rep(i, n){
        auto [c, d] = vg[i];
        dist[i][i+n] = 1;
        dist[i+n][2*n+1] = h+w-c-d;
        rep(j, n){
            auto [a, b] = vst[j];
            dist[i+n][j] = abs(c-a) + abs(d-b);
        }
    }
    rep(i, n){
        auto [a, b] = vst[i];
        dist[2*n][i] = a+b-2;
        dist[i][2*n+1] = h+w-a-b;
    }
    dist[2*n][2*n+1] = h+w-2;

    vvi adj(2*n+2);
    rep(i, 2*n+2){
        rep(j, 2*n+2){
            if(dist[i][j] < inf)adj[i].push_back(j);
        }
    }

    vi ans(2*n+2, inf);
    ans[2*n] = 0;
    priority_queue<p, vector<p>, greater<p>> pq;
    pq.push({0, 2*n});
    while(!pq.empty()){
        p u = pq.top(); pq.pop();
        if(u.first > ans[u.second])continue;
        for(auto v : adj[u.second]){
            int alt = u.first + dist[u.second][v];
            if(alt < ans[v]){
                ans[v] = alt;
                pq.push({alt, v});
            }
        }
    }

    cout << ans[2*n+1] << endl;
    return 0;
}