#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef std::pair<long long, long long> P;

int main()
{
    ll h, w, n;
    cin >> h >> w >> n;
    queue<P> que;
    for (int i = 1; i <= h; ++i) {
        for (int j = 1; j <= w; ++j) que.push({i, j});
    }
    for (int i = 0; i < n; ++i) {
        queue<P> nq;
        ll r1, c1, r2, c2;
        cin >> r1 >> c1 >> r2 >> c2;
        while (!que.empty()) {
            ll f = que.front().first;
            ll s = que.front().second;
            que.pop();
            if (r1 > f || f > r2 || c1 > s || s > c2) nq.push({f, s});
        }
        swap(que, nq);
    }
    cout << que.size() << endl;
}