#include<bits/stdc++.h>
using namespace std;
template<typename T>
vector<T> dijkstra(vector<vector<pair<int,T>>>&g, const T INF, int s=0)
{
    int n=g.size();
    vector<T>dist(n,INF);
    dist[s]=0;
    priority_queue<pair<T,int>,vector<pair<T,int>>,greater<pair<T,int>>>q;
    q.push(make_pair(T(0),s));
    while(!q.empty())
    {
        auto[d,u]=q.top();
        q.pop();
        if(dist[u]<d)continue;
        for(auto[v,w]:g[u])
        {
            if(dist[v]>d+w)
            {
                dist[v]=d+w;
                q.push(make_pair(dist[v],v));
            }
        }
    }
    return dist;
}
long H,W,N,A[2020],B[2020];
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cin>>H>>W>>N;
    for(int i=0;i<N;i++)cin>>A[i]>>B[i]>>A[i+N]>>B[i+N];
    vector<vector<pair<int,long>>>G(2*N+2);
    for(int i=0;i<2*N;i++)for(int j=0;j<2*N;j++)if(i!=j)
    {
        if(i+N==j)G[i].push_back(make_pair(j,1));
        else G[i].push_back(make_pair(j,abs(A[j]-A[i])+abs(B[j]-B[i])));
    }
    for(int i=0;i<2*N;i++)
    {
        G[2*N].push_back(make_pair(i,A[i]+B[i]-2));
        G[i].push_back(make_pair(2*N+1,H+W-A[i]-B[i]));
    }
    G[2*N].push_back(make_pair(2*N+1,H+W-2));
    cout<<(dijkstra(G,1L<<60,2*N)[2*N+1])<<endl;
}