#ifndef INCLUDED_MAIN
#define INCLUDED_MAIN

#include __FILE__

using namespace nskr;


int main(void){
    ll h, w; cin >> h >> w;
    ll n; cin >> n;
    vector<vector<bool>> t(h,vector<bool>(w,true));
    vector<vector<ll>> mxc(h,vector<ll>(w,-1)), mxd(h,vector<ll>(w,-1));
    for(;n--;){
        ll a,b,c,d; cin >> a >> b >> c >> d;
        a--;b--;c--;d--;

        if(mxc[a][b] >= c && mxd[a][b] >= d){
            continue;
        }


        for(ll i=a; i<=c; i++){
            for(ll j=b; j<=d; j++){
                t[i][j] = false;
                        
                mxc[i][j] = max(mxc[i][j], c);
                mxd[i][j] = max(mxd[i][j], d);
            
            }
        }
        mxc[a][b] = max(mxc[a][b], c);
        mxd[a][b] = max(mxd[a][b], d);
    }

    ll i,j, ans = 0;
    rep(i,h){
        rep(j,w){
            if(t[i][j]) ans++;
         }
    }
    cout << ans << "\n";
}

#else
#include <bits/stdc++.h>
using namespace std;

using ll = long long;
using ld=  long double;
#define rep(i,n) for(i=0;i<(n);i++)
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()

namespace nskr{}

int randint(int a, int b){
    static mt19937 gen(chrono::steady_clock::now().time_since_epoch().count());
    uniform_int_distribution<int> dist(a,b);
    return dist(gen);
}


#endif