/*
TASK:SIENAJ
LANG:C++
*/
#include <cstdio>

int main()
{
	FILE *fin = fopen("SIENA.IN", "r");
	int w, h;
	fscanf(fin, "%d%d", &w, &h);
	int n;
	fscanf(fin, "%d", &n);
	int area = w*h;
	for (int i = 0; i < n; ++i) {
		int x1, y1, x2, y2;
		fscanf(fin, "%d%d%d%d", &x1, &y1, &x2, &y2);
		area -= (x2-x1) * (y2-y1);
	}
	fclose(fin);
	FILE *fout = fopen("SIENA.OUT", "w");
	fprintf(fout, "%d\n", area);
	fclose(fout);
	return 0;
}