#include<bits/stdc++.h>
using namespace std;
#include<atcoder/all>
using namespace atcoder;
#define rep(i,n) for (int i = 0; i < (n); ++i)
using ld = long double;
using ll = long long;

template<class T> bool chmax(T &a, T b)
{
	if(a<b)
	{
	a = b;
	return true;
	}
	return false;
}
template<class T> bool chmin(T &a, T b)
{
	if(a>b)
	{
		a = b;
		return true;
	}
	return false;
}

int H, W, N, A[1<<10][4];
using P = pair<ll,ll>;

int main()
{
	cin >> H >> W >> N;
	rep(i,N) rep(j,4) cin >> A[i][j];

	int M = 2*N+2;
	ll G[M][M] = {};
	rep(i,M) rep(j,M) G[i][j] = 1e18;
	rep(i,2*N) rep(j,2*N) if(i!=j)
	{
		int a = (i&1?2:0);
		int b = (j&1?2:0);
		G[i][j] = abs(A[i/2][a]-A[j/2][b]) + abs(A[i/2][a+1]-A[j/2][b+1]);
	}
	rep(i,N) G[2*i][2*i+1] = 1;
	rep(i,2*N)
	{
		int a = (i&1?2:0);
		G[2*N][i] = G[i][2*N] = A[i/2][a] + A[i/2][a+1] - 2;
		G[2*N+1][i] = G[i][2*N+1] = H-A[i/2][a] + W-A[i/2][a+1];
	}

	priority_queue<P, vector<P>, greater<P>> q;
	q.push({0,2*N});
	vector<ll> dist(2*N+2, 1e18);
	dist[2*N] = 0;
	while(!q.empty())
	{
		auto [c,v] = q.top();
		q.pop();
		if(dist[v]<c) continue;
		rep(nv,2*N+2) if(nv!=v && G[v][nv]<1e18)
		{
			if(chmin(dist[nv], dist[v]+G[v][nv])) q.push({dist[nv], nv});
		}
	}
	//rep(i,M) cout << dist[i] << endl;
	cout << dist[2*N+1] << endl;
}