#line 2 "kyopro_lib/template/template.hpp"
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define all(x) (x).begin(), (x).end()
template <typename T, typename U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
    os << p.first << " " << p.second;
    return os;
}
ll sum(vector<ll> a){
    ll res = 0;
    for(auto x:a) res += x;
    return res;
}
template <typename T, typename U>
istream &operator>>(istream &is, pair<T, U> &p) {
    is >> p.first >> p.second;
    return is;
}

template <typename T>
ostream &operator<<(ostream &os, const vector<T> &v) {
    ll s = (ll)v.size();
    for (ll i = 0; i < s; i++) os << (i ? " " : "") << v[i];
    return os;
}
template <typename T>
istream &operator>>(istream &is, vector<T> &v) {
    for (auto &x : v) is >> x;
    return is;
}
#define rep(i, n) for (ll (i) = 0; (i) < (ll)(n); (i)++)
#line 2 "main.cpp"
signed main(){
    ll H,W,N;
    cin >> H >> W >> N;
    H--;W--;
    map<pair<ll,ll>,ll> mp;
    priority_queue<pair<ll,pair<pair<ll,ll>,pair<ll,ll>>>, vector<pair<ll,pair<pair<ll,ll>,pair<ll,ll>>>>, greater<pair<ll,pair<pair<ll,ll>,pair<ll,ll>>>>> q;
    rep(i,N)
    {
        ll a,b,c,d;
        cin >> a >> b >> c >> d;
        a--;b--;c--;d--;
        q.push({a+b,{{a,b},{c,d}}});
    }
    ll finaly = H+W;
    while(!q.empty())
    {
        auto [_,p] = q.top();
        q.pop();
        auto [a,b] = p.first;
        auto [c,d] = p.second;
        if (mp[{a,b}] == 0)
        {
            mp[{a,b}] = a+b;
        }else
        {
            mp[{a,b}] = min(a+b,mp[{a,b}]);
        }
        if (mp[{c,d}] == 0)
        {
            mp[{c,d}] = min(c+d,mp[{a,b}]+1);
        }else
        {
            mp[{c,d}] = min(c+d,min(mp[{c,d}],mp[{a,b}]+1));
        }
        finaly = min(finaly,H+W-c-d+mp[{c,d}]);
        finaly = min(finaly,H+W-a-b+mp[{a,b}]);
    }
    cout << finaly << endl;
}