fn main() {
    input!{
        h: usize, w: usize, n: usize,
        abcd: [(usize, usize, usize, usize); n],
    }

    // 頂点情報
    // (WarpのS,G * n S, G)
    let sz = 2 + n*2;
    let mut p = vec![(0, 0); sz];
    for i in 0..n {
        p[2*i] = (abcd[i].0, abcd[i].1);
        p[2*i+1] = (abcd[i].2, abcd[i].3);
    }
    p[sz-2] = (1, 1);
    p[sz-1] = (h, w);

    // costの隣接行列を用意
    const INF: usize = 1 << 60;
    let mut cost_t = vec![vec![INF; sz]; sz];
    for i in 0..sz {
        for j in 0..sz {
            let cost = p[i].0.abs_diff(p[j].0) + p[i].1.abs_diff(p[j].1);
            cost_t[i][j] = min(cost_t[i][j], cost);
        }
    }
    for i in 0..n {
        cost_t[2*i][2*i+1] = min(cost_t[2*i][2*i+1], 1);
    }

    // s -> gへのダイクストラ
    // hp = 最短距離、頂点
    let mut hp = BinaryHeap::new();
    hp.push(Reverse((0, sz-2)));
    
    let mut used = vec![false; sz];
    let mut dist = vec![INF; sz];

    while hp.len() > 0 {
        let (cdist, cp) = hp.pop().unwrap().0;
        if used[cp] { continue; }

        used[cp] = true;
        
        for j in 0..sz {
            let cost = cost_t[cp][j];

            if cdist + cost < dist[j] {
                dist[j] = cdist + cost;
                hp.push(Reverse((dist[j], j)));
            }
        }
    }

    println!("{}", dist[sz-1]);
}
// ---------- begin input macro ----------
#[macro_export]
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

#[macro_export]
macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};
    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

#[macro_export]
macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };
    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };
    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };
    ($iter:expr, bytes) => {
        read_value!($iter, String).bytes().collect::<Vec<u8>>()
    };
    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };
    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}
// ---------- end input macro ----------
#[allow(unused)]
use std::{
	io::stderr, io::stdin, io::BufRead, io::Write,
	mem::swap,
	cmp::min, cmp::max,
	cmp::Reverse,
	collections::HashSet, collections::BTreeSet,
	collections::HashMap, collections::BTreeMap,
	collections::BinaryHeap,
	collections::VecDeque,
};