#include <iostream>
#include <algorithm>
#include <cstdio>

using namespace std;

int main() {
	int n, minx, miny, maxx, maxy;
	cin >> n >> minx >> miny >> maxx >> maxy;
	for (int i = 1; i < n; i++)	{
		int minxa, minya, maxxa, maxya;
		cin >> minxa >> minya >> maxxa >> maxya;
		minx = max(minx, minxa);
		miny = max(miny, minya);
		maxx = min(maxx, maxxa);
		maxy = min(maxy, maxya);
	}
	cout << (int64_t)max(0, maxx - minx) * max(0, maxy - miny) << endl;
}