#ifndef INCLUDED_MAIN
#define INCLUDED_MAIN

#include __FILE__

using namespace nskr;

struct sg{
    vector<int> v;
    int w;
    sg(int n, int x){
        w=1;
        while(w<n) w<<=1;
        v.resize(w*2, 0);
        for(int i=0; i<n;i++) set(i,x);

    }

    void set(int n, int x){
        v[w+n] = x;
        int p = ((w+n)>>1);
        while(true){
            v[p] = v[p*2] + v[p*2+1];
            p>>=1;
            if(p==0) break;

        }
    }

    int prod(int l, int r){
        if(l!=0){
            return prod(0,r) - prod(0,l);
        }
        int ret = 0;
        int i=1,j=w,k=0;
        while(true){
            while(k+(i<<1) < r) {
                i<<=1;
                j>>=1;
            }
            ret += v[j];
            k += i;
            if(k==r) break;
            i=1;
            j=w+k;
        }
        return ret;
    }

};
int main(void){
    ll h, w; cin >> h >> w;
    ll n; cin >> n;
    vector<sg> s(h,sg(w,1));

    for(;n--;){
        int a,b,c,d; cin >> a >> b >> c >> d;
        a--;b--;c--;d--;
        
        for(int i=a; i<=c; i++){
            if(s[i].prod(b,d+1) == 0) continue;
            for(int j=b; j<=d; j++){
                s[i].set(j,0);
            }
        }
    }

    int i, ans = 0;
    rep(i,h){
        ans += s[i].v[1];
    }
    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