#include <bits/stdc++.h>
using namespace std;
int main() {
  int w, h, n, x, y, a;
  int w0 = 0, h0 = 0;
  cin >> w >> h >> n;
  for (int i = 0; i < n; i++) {
    cin >> x >> y >> a;
    if (a == 1 & w0 < x) w0 = x;
    if (a == 2 & w > x) w = x;
    if (a == 3 & h0 < y) h0 = y;
    if (a == 4 & h > y) h = y;
  }
  if ((w < w0) | (h < h0))
    cout << 0 << endl;
  else
    cout << (w - w0) * (h - h0) << endl;
}
