#include <iostream>
#include <vector>
#include <queue>
#include <utility>
using namespace std;
using ll = long long;
using Graph = vector<vector<pair<int, ll>>>;
using pli = pair<ll, int>;

struct point{
    ll x, y;

    ll distance(point q){
        return abs(x-q.x)+abs(y-q.y);
    }
};

const ll INF = 1LL<<60;

int N;

point pos[2010];
ll G[2010][2010];
ll D[2010];

void Dijkstra(int src){
    fill(&D[0], &D[0]+2010, INF);
    D[src]=0LL;
    priority_queue<pli, vector<pli>, greater<pli>> Q;
    Q.push({0LL, src});

    while(! Q.empty()){
        auto [dist, cur] = Q.top();
        Q.pop();
        if (dist>D[cur]) continue;
        for (int dst=0;dst<2*N+2;dst++){
            if (dist+G[cur][dst]<D[dst]){
                D[dst]=dist+G[cur][dst];
                Q.push({D[dst], dst});
            }
        }
    }
}

int main(){
    ll H, W;
    cin>>H>>W>>N;
    pos[0]={1LL, 1LL}, pos[1]={H, W};
    for (int i=1;i<=N;i++){
        cin>>pos[2*i].x>>pos[2*i].y>>pos[2*i+1].x>>pos[2*i+1].y;
    }
    for (int i=0;i<2*N+2;i++){
        for (int j=i;j<2*N+2;j++){
            G[i][j]=pos[i].distance(pos[j]);
            G[j][i]=G[i][j];
        }
    }
    for (int i=1;i<=N;i++) G[2*i][2*i+1]=1;

    Dijkstra(0);
    cout << D[1] << "\n";

    return 0;
}