#include <iostream>
#include <vector>

using namespace std;
// 愚直解(TLE解法) θ(NHW)
int main() {
    int H, W, N;
    cin >> H >> W >> N;

    vector<vector<bool>> grid(H, vector<bool>(W, false));

    for (int i = 0; i < N; ++i) {
        int r1, c1, r2, c2;
        cin >> r1 >> c1 >> r2 >> c2;
        r1--; c1--; r2--; c2--;
        for (int r = r1; r <= r2; ++r) {
            for (int c = c1; c <= c2; ++c) {
                grid[r][c] = true;
            }
        }
    }

    int ans = 0;
    for (int r = 0; r < H; ++r) {
        for (int c = 0; c < W; ++c) {
            if (!grid[r][c]) {
                ans++;
            }
        }
    }

    cout << ans << endl;

    return 0;
}