#include<bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;
using mint=modint998244353; //1000000007;
using ll=long long;
using pp=pair<int,int>;
#define sr string 
#define vc vector
#define fi first
#define se second
#define rep(i,n) for(int i=0;i<(int)n;i++)
#define pb push_back
#define all(v) v.begin(),v.end()
#define pque priority_queue
#define bpc(a) __builtin_popcount(a)
int main(){
  int h,w,n;cin>>h>>w>>n;
  vc<pp>g;
  vc v(0,vc<int>(0));
  map<pp,int>m;
  auto f=[&](pp p)->void{
    if(m.count(p))return;
    m[p]=g.size();
    g.pb(p);
    v.pb(vc<int>(0));
    return;
  };
  f({0,0}); f({h-1,w-1});
  rep(i,n){
    pp a,b;
    cin>>a.fi>>a.se>>b.fi>>b.se;
    a.fi--,a.se--,b.fi--,b.se--;
    f(a); f(b);
    v[m[a]].pb(m[b]);
  }
  n=g.size();
  vc<ll>d(n,1e18);
  pque<pair<ll,int>>q;
  q.push({0,0});
  while(q.size()){
    auto [xx,a]=q.top(); q.pop();
    xx=-xx;
    if(xx>=d[a])continue;
    d[a]=xx;
    for(auto au:v[a])q.push({-d[a]-1,au});
    rep(i,n)if(i!=a){
      ll x=(ll)abs(g[i].fi-g[a].fi)+abs(g[i].se-g[a].se);
      q.push({-d[a]-x,i});
    }
  }
  //rep(i,n)cout<<d[i]<<' ';
  cout<<d[1];
}