#ifndef INCLUDED_MAIN
#define INCLUDED_MAIN

#include __FILE__

using namespace nskr;


int main(void){
    int h, w; cin >> h >> w;
    int n; cin >> n;
    vector<vector<bool>> t(h+1,vector<bool>(w+1,true));
    vector<vector<int>> im(h+1,vector<int>(w+1,1));
    int i,j, ans = 0;

    rep(i,h){
        rep(j,w) im[i+1][j+1] += im[i][j+1] + im[i+1][j] - im[i][j];
    }

    for(;n--;){
        int a,b,c,d; cin >> a >> b >> c >> d;
        a--;b--;c--;d--;

        if(im[c+1][d+1] - im[c+1][b] - im[a][d+1] + im[a][b] == 0){
            continue;
        }

        for(int i=a; i<=c; i++){
            for(int j=b; j<=d; j++){
                t[i][j] = false;
            }
        }

        for(int i=a; i<=h; i++){
            for(int j=b; j<=w; j++){
                if(i+j == 0) im[i][j] = (t[i][j]?1:0) ;
                else if(i == 0) im[i][j] = (t[i][j]?1:0) + im[i][j-1];
                else if(j == 0) im[i][j] = (t[i][j]?1:0) + im[i][j-1];
                else im[i][j] = (t[i][j]?1:0) + im[i][j-1] + im[i-1][j] - im[i-1][j-1];
            }
        }
    }

    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