#include <bits/stdc++.h>

int ri() {
	int n;
	scanf("%d", &n);
	return n;
}

int main() {
	int n = ri();
	int a[n][4];
	std::set<int> xs, ys;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < 4; j++) a[i][j] = ri();
		xs.insert(a[i][0]);
		xs.insert(a[i][2]);
		ys.insert(a[i][1]);
		ys.insert(a[i][3]);
	}
	std::map<int, int> compx, compy;
	std::vector<int> decompx, decompy;
	int cntx = 0, cnty = 0;
	for (auto i : xs) compx[i] = cntx++, decompx.push_back(i);
	for (auto i : ys) compy[i] = cnty++, decompy.push_back(i);
	std::vector<int> diff[cntx + 1];
	for (int i = 0; i <= cntx; i++) diff[i].resize(cnty + 1, 0);
	for (int i = 0; i < n; i++) {
		int x1 = compx[a[i][0]];
		int x2 = compx[a[i][2]];
		int y1 = compy[a[i][1]];
		int y2 = compy[a[i][3]];
		diff[x1][y1]++;
		diff[x1][y2]--;
		diff[x2][y1]--;
		diff[x2][y2]++;
	}
	for (int i = 0; i <= cntx; i++) for (int j = 0; j < cnty; j++) diff[i][j + 1] += diff[i][j];
	for (int i = 0; i < cntx; i++) for (int j = 0; j <= cnty; j++) diff[i + 1][j] += diff[i][j];
	int64_t res = 0;
	for (int i = 0; i < cntx; i++) for (int j = 0; j < cnty; j++) if (diff[i][j]) {
		res += (int64_t)(decompx[i + 1] - decompx[i]) * (decompy[j + 1] - decompy[j]);
	}
	std::cout << res << std::endl;
	
	return 0;
}

