// -*- coding:utf-8-unix -*-
// #![feature(map_first_last)]
#![allow(dead_code)]
#![allow(unused_imports)]
#![allow(unused_macros)]
// use core::num;
use std::cmp::*;
use std::fmt::*;
use std::hash::*;
use std::iter::FromIterator;
use std::*;
use std::{cmp, collections, fmt, io, iter, ops, str};
const INF: i64 = 1223372036854775807;
const UINF: usize = INF as usize;
const LINF: i64 = 2147483647;
const INF128: i128 = 1223372036854775807000000000000;
const MOD1: i64 = 1000000007;
const MOD9: i64 = 998244353;
const MOD: i64 = MOD9;
// const MOD: i64 = MOD2;
const UMOD: usize = MOD as usize;
const M_PI: f64 = 3.14159265358979323846;

// use proconio::input;
// const MOD: i64 = INF;

use cmp::Ordering::*;
use std::collections::*;

use std::io::stdin;
use std::io::stdout;
use std::io::Write;

macro_rules! p {
    ($x:expr) => {
        //if expr
        println!("{}", $x);
    };
}

macro_rules! vp {
    // vector print separate with space
    ($x:expr) => {
        println!(
            "{}",
            $x.iter()
                .map(|x| x.to_string())
                .collect::<Vec<_>>()
                .join(" ")
        );
    };
}

macro_rules! d {
    ($x:expr) => {
        eprintln!("{:?}", $x);
    };
}
macro_rules! yn {
    ($val:expr) => {
        if $val {
            println!("Yes");
        } else {
            println!("No");
        }
    };
}

macro_rules! map{
    // declear btreemap
    ($($key:expr => $val:expr),*) => {
        {
            let mut map = ::std::collections::BTreeMap::new();
            $(
                map.insert($key, $val);
            )*
            map
        }
    };
}

macro_rules! set{
    // declear btreemap
    ($($key:expr),*) => {
        {
            let mut set = ::std::collections::BTreeSet::new();
            $(
                set.insert($key);
            )*
            set
        }
    };
}

fn main() {
    solve();
}

// use str::Chars;
#[allow(dead_code)]
fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

#[allow(dead_code)]
fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}

#[allow(dead_code)]
fn read_mat<T: std::str::FromStr>(n: u32) -> Vec<Vec<T>> {
    (0..n).map(|_| read_vec()).collect()
}

#[allow(dead_code)]
fn readii() -> (i64, i64) {
    let mut vec: Vec<i64> = read_vec();
    (vec[0], vec[1])
}

#[allow(dead_code)]
fn readiii() -> (i64, i64, i64) {
    let mut vec: Vec<i64> = read_vec();
    (vec[0], vec[1], vec[2])
}
#[allow(dead_code)]
fn readuu() -> (usize, usize) {
    let mut vec: Vec<usize> = read_vec();
    (vec[0], vec[1])
}

#[allow(dead_code)]
fn readff() -> (f64, f64) {
    let mut vec: Vec<f64> = read_vec();
    (vec[0], vec[1])
}

fn readcc() -> (char, char) {
    let mut vec: Vec<char> = read_vec();
    (vec[0], vec[1])
}

fn readuuu() -> (usize, usize, usize) {
    let mut vec: Vec<usize> = read_vec();
    (vec[0], vec[1], vec[2])
}
#[allow(dead_code)]
fn readiiii() -> (i64, i64, i64, i64) {
    let mut vec: Vec<i64> = read_vec();
    (vec[0], vec[1], vec[2], vec[3])
}

#[allow(dead_code)]
fn readuuuu() -> (usize, usize, usize, usize) {
    let mut vec: Vec<usize> = read_vec();
    (vec[0], vec[1], vec[2], vec[3])
}

fn read_imat(h: usize) -> Vec<Vec<i64>> {
    (0..h).map(|_| read_vec()).collect()
}
fn read_cmat(h: usize) -> Vec<Vec<char>> {
    (0..h).map(|_| read::<String>().chars().collect()).collect()
}

fn dijkstra(graph: &Vec<Vec<(usize, usize)>>, start: usize) -> Vec<usize> {
    let mut dist = vec![INF as usize; graph.len()];
    let mut heap = BinaryHeap::new();
    heap.push(Reverse((0 as usize, start)));
    dist[start] = 0;
    while let Some(Reverse(x)) = heap.pop() {
        let cost = x.0;
        let v = x.1;
        if cost > dist[v] {
            continue;
        }
        for edge in &graph[v] {
            let nc = cost + edge.1;
            let nv = edge.0;
            if nc < dist[nv] {
                heap.push(Reverse((nc, nv)));
                dist[nv] = nc;
            }
        }
    }
    return dist;
}
fn solve() {
    let (h, w, n) = readuuu();
    let mut node = set![];
    node.insert((0, 0));
    node.insert((h as i64 - 1, w as i64 - 1));
    let mut data = vec![];
    for i in 0..n {
        let (a, b, c, d) = readiiii();
        data.push((a - 1, b - 1, c - 1, d - 1));
        node.insert((a - 1, b - 1));
        node.insert((c - 1, d - 1));
    }
    let node_num = node.len();
    let mut node_to_idx = map![];
    let mut idx_to_node = vec![];
    let mut src_idx = 0;
    let mut dst_idx = 0;
    for (i, &x) in node.iter().enumerate() {
        node_to_idx.insert(x, i);
        idx_to_node.push(x);
        if x == (0, 0) {
            src_idx = i;
        }
        if x == (h as i64 - 1, w as i64 - 1) {
            dst_idx = i;
        }
    }
    let mut graph = vec![vec![(0 as usize, 0 as usize); (0) as usize]; (node_num) as usize];
    for i in 0..data.len() {
        let (a, b, c, d) = data[i];
        let i1 = node_to_idx[&(a, b)];
        let i2 = node_to_idx[&(c, d)];
        // let dist = ((a as i64 - c as i64).abs() + (b as i64 - d as i64).abs()) as usize;
        graph[i1].push((i2, 1));
    }
    for i in 0..node_num {
        for j in 0..node_num {
            let (a, b) = idx_to_node[i];
            let (c, d) = idx_to_node[j];
            let dist = ((a as i64 - c as i64).abs() + (b as i64 - d as i64).abs()) as usize;
            graph[i].push((j, dist));
        }
    }
    let dist = dijkstra(&graph, src_idx);
    p!(dist[dst_idx]);
    return;
}