#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;
using ll = long long;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;
using VD = vector<double>;
using VVD = vector<VD>;
using VS = vector<string>;
using P = pair<ll,ll>;
using VP = vector<P>;
#define rep(i, n) for (ll i = 0; i < ll(n); i++)
#define out(x) cout << x << endl
#define dout(x) cout << fixed << setprecision(10) << x << endl
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()
#define sz(x) (int)(x.size())
#define re0 return 0
#define pcnt __builtin_popcountll
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
constexpr int inf = 1e9;
constexpr ll INF = 1e18;
//using mint = modint1000000007;
using mint = modint998244353;
int di[4] = {1,0,-1,0};
int dj[4] = {0,1,0,-1};

int main(){
    ll h,w,n;
    cin >> h >> w >> n;
    VL a(n),b(n),c(n),d(n);
    rep(i,n){
        cin >> a[i] >> b[i] >> c[i] >> d[i];
    }
    n++;
    a.emplace_back(h);
    b.emplace_back(w);
    c.emplace_back(1);
    d.emplace_back(1);
    VVL dist(n*2,VL(n*2,INF));
    rep(i,n)rep(j,n){
        //ig->js
        dist[i*2+1][j*2] = abs(c[i]-a[j])+abs(d[i]-b[j]);
        //jg->is
        dist[j*2+1][i*2] = abs(a[i]-c[j])+abs(d[j]-b[i]);
    }
    rep(i,n){
        dist[i*2][i*2+1] = 1;
        dist[i*2+1][i*2] = abs(a[i]-c[i])+abs(b[i]-d[i]);
    }
    VL dist0(n*2,INF);
    dist0[(n-1)*2+1] = 0;
    priority_queue<P,VP,greater<P>> pq;
    pq.emplace(dist0[(n-1)*2+1],(n-1)*2+1);
    while(sz(pq)){
        auto [d,v] = pq.top();
        pq.pop();
        if(dist0[v] < d) continue;
        rep(i,n*2){
            if(chmin(dist0[i],dist0[v]+dist[v][i])){
                pq.emplace(dist0[i],i);
            }
        }
    }
    out(dist0[(n-1)*2]);
}