#include <bits/stdc++.h>
using namespace std;

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    long long H,W; cin >> H >> W;
    int N; cin >> N;
    map<pair<int,int>,pair<int,int>> Graph;
    map<pair<int,int>,int> dist;
    for(int i=0; i<N; i++){
        int a,b,c,d; cin >> a >> b >> c >> d;
        Graph[{a,b}] = {c,d};
        dist[{a,b}] = 2e9+9; dist[{c,d}] = 2e9+9;
    }
    dist[{1,1}] = 0; dist[{H,W}] = 2e9+9;
    priority_queue<tuple<int,int,int>,vector<tuple<int,int,int>>,greater<>> Q;
    Q.push({0,1,1});
    while(Q.size()){
        auto [d,x,y] = Q.top(); Q.pop();
        if(dist[{x,y}] > d) continue;

        auto [x2,y2] = Graph[{x,y}];
        if(x2 != 0) if(dist[{x2,y2}] > d+1) dist[{x2,y2}] = d+1,Q.push({d+1,x2,y2});
        
        for(auto [p,d3] : dist){
            auto [x3,y3] = p;
            long long nc = d;
            nc += abs(x-x3); nc += abs(y-y3);
            if(nc < d3) dist[p] = nc,Q.push({nc,x3,y3});
        }  
    }
    


    cout << dist[{H,W}] << endl;
}