#include <bits/stdc++.h>
using namespace std;
int main(){
    long long H,W;
    int N;
    cin >> H >> W >> N;
    vector<long long> a(N), b(N), c(N),d(N);
    for(int i = 0; i < N;i++){
        cin >> a[i] >> b[i] >> c[i] >> d[i];
    }

    vector<vector<long long>> G(N+2, vector<long long>(N+2, -1));
    for(int i = 0; i < N;i++){
        G[0][i+1] = a[i] + b[i] - 1;
    }
    G[0][N+1] = H + W - 2;
    for(int i = 0; i < N;i++){
        for(int j = 0; j < N; j++){
            if(i == j){
                continue;
            }
            G[i+1][j+1] = abs(a[j] - c[i])+ abs(b[j] - d[i]) + 1;
        }
    }
    for(int i = 0; i < N;i++){
        G[i+1][N+1] = H - c[i] + W - d[i];
    }

    priority_queue<pair<long long,int>, vector<pair<long long,int>>, greater<pair<long long,int>>> que;
    que.push({0, 0});
    vector<long long> ans(N+2, 3e18);
    ans[0] = 0;
    while(!que.empty()){
        pair<long long, int> v = que.top();
        long long x = v.first;
        int y = v.second;
        que.pop();
        for(int i = 0; i < N + 2;i++){
            if(G[y][i] == -1 || ans[i] <= x + G[y][i]){
                continue;
            }
            ans[i] = x + G[y][i];
            que.push({x + G[y][i], i});
        }
    }
    cout << ans[N+1] << endl;
}