#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <algorithm>
#include <cmath>
#include <vector>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <queue>
#include <ctime>
#include <cassert>
#include <complex>
#include <string>
#include <cstring>
#include <chrono>
#include <random>
#include <bitset>
#include <fstream>
#include <array>
#include <functional>
#include <stack>
#include <memory>
using namespace std;
#define int long long
#define ii pair <int, int>
#define app push_back
#define all(a) a.begin(), a.end()
#define bp __builtin_popcountll
#define ll long long
#define mp make_pair
#define x first
#define y second
#define Time (double)clock()/CLOCKS_PER_SEC
#define munq(a) sort(all(a)); a.resize(unique(all(a))-a.begin())
#define sz(a) ((int)a.size())

#ifdef LOCAL
#define debug(...) [](auto...a){ ((cerr << a << ' '), ...) << endl; }(#__VA_ARGS__, ":", __VA_ARGS__)
#else
#define debug(...)
#endif

#define FORI(i,a,b) for (int i = (a); i < (b); ++i)
#define FOR(i,a) FORI(i,0,a)
#define ROFI(i,a,b) for (int i = (b)-1; i >= (a); --i)
#define ROF(i,a) ROFI(i,0,a)
#define rep(a) FOR(_,a)
#define each(a,x) for (auto& a: x)
#define FORN(i, n) FORI(i, 1, n + 1)

using vi = vector<int>;
template <typename T>
std::istream& operator >>(std::istream& input, std::pair <T, T> & data)
{
    input >> data.x >> data.y;
    return input;
}
template <typename T>
std::istream& operator >>(std::istream& input, std::vector<T>& data)
{
    for (T& x : data)
        input >> x;
    return input;
}
template <typename T>
std::ostream& operator <<(std::ostream& output, const pair <T, T> & data)
{
    output << "(" << data.x << "," << data.y << ")";
    return output;
}
template <typename T>
std::ostream& operator <<(std::ostream& output, const std::vector<T>& data)
{
    for (const T& x : data)
        output << x << " ";
    return output;
}
ll div_up(ll a, ll b) { return a/b+((a^b)>0&&a%b); } // divide a by b rounded up
ll div_down(ll a, ll b) { return a/b-((a^b)<0&&a%b); } // divide a by b rounded down 
ll math_mod(ll a, ll b) { return a - b * div_down(a, b); }
#define tcT template<class T
#define tcTU tcT, class U
tcT> using V = vector<T>; 
tcT> bool ckmin(T& a, const T& b) {
    return b < a ? a = b, 1 : 0; 
} // set a = min(a,b)
tcT> bool ckmax(T& a, const T& b) {
    return a < b ? a = b, 1 : 0; 
}
tcT> vector <T> presum(vector <T> &a) {
    vector <T> p(a.size() + 1);
    FOR (i, a.size()) {
        p[i + 1] = p[i] + a[i];
    }   
    return p;
}
tcT> vector <T> sufsum(vector <T> &a) {
    vector <T> p(a.size() + 1);
    for (int i = (int)a.size() - 1; i >= 0; --i) {
        p[i] = p[i + 1] + a[i];
    }
    return p;
}
ll gcd(ll a, ll b) {
    while (b) {
        tie(a, b) = mp(b, a % b);
    }
    return a;
}
int Bit(int mask, int bit) { return (mask >> bit) & 1; }
signed main() {
    #ifdef LOCAL
    #else
    #define endl '\n'
    ios_base::sync_with_stdio(0); cin.tie(0);
    #endif
    int h, w, no;
    cin >> h >>w>>no;
    V <ii> p;
    V <pair <ii, ii> > E;
    FOR(i,no) {
        int a, b, c, d; cin >> a >> b >> c >> d;
        E.app({{a,b},{c,d}});
        p.app({a,b});p.app({c,d});
    }

    p.app({1,1});p.app({h,w});
    munq(p);

    int ve = sz(p);
    V <vi> g(ve, vi(ve));
    FOR(i,ve) {
        FOR(j,ve) {
            g[i][j] = abs(p[i].x-p[j].x)+abs(p[i].y-p[j].y);
        }
    }

    for (auto [u, v] : E) {
        int i = lower_bound(all(p),u)-p.begin(), j = lower_bound(all(p),v)-p.begin();
        debug(i,j,ve,g[i][j]);
        g[i][j]=1;
    }

    const int inf =1e18;
    vi dist(ve, inf);

    dist[0]=0;
    vi used(ve);
    rep(ve) {
        int u = -1;
        FOR(i,ve){
            if (!used[i]&&(u==-1||dist[i]<dist[u])) {
                u = i;
            }
        }
        debug(p[u],dist[u]);
        used[u] = 1;
        FOR(v,ve){
            ckmin(dist[v],dist[u]+g[u][v]);
        }
    }
    cout<<dist.back()<<endl;
}