#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include<bits/stdc++.h>
#include<atcoder/all>
using namespace std;
using namespace atcoder;
using ll=long long;
using P=pair<ll,ll>;

void IO(){
  ios::sync_with_stdio(false);
  std::cin.tie(nullptr);
}

int main(){
  IO();
  ll h,w,n;
  cin>>h>>w>>n;
  vector<ll> a(n),b(n),c(n),d(n);
  for(ll i=0;i<n;i++){
    cin>>a[i]>>b[i]>>c[i]>>d[i];
  }
  vector<vector<ll>> G(n+2,vector<ll>(n+2,-1));
  for(ll i=0;i<n;i++){
    G[0][i+1]=a[i]+b[i]-1;
  }
  G[0][n+1]=h+w-2;
  for(ll i=0;i<n;i++){
    for(ll j=0;j<n;j++){
      if(i!=j){
        G[i+1][j+1]=abs(a[j]-c[i])+abs(b[j]-d[i])+1;
      }
    }
  }
  for(ll i=0;i<n;i++){
    G[i+1][n+1]=h+w-c[i]-d[i];
  }
  priority_queue<P,vector<P>,greater<P>> que;
  que.push(P(0,0));
  vector<ll> dist(n+2,1e18);
  dist[0]=0;
  while(que.size()){
    P q=que.top();
    que.pop();
    ll x=q.first;
    ll y=q.second;
    for(ll i=0;i<=n+1;i++){
      if(G[y][i]==-1){
        continue;
      }
      if(dist[i]<=x+G[y][i]){
        continue;
      }
      dist[i]=x+G[y][i];
      que.push(P(x+G[y][i],i));
    }
  }
  cout<<dist[n+1]<<endl;
}