#include <cstdio>#include <algorithm>#include <cstring>#include <vector>typedef long long LL;using namespace std;#define lson rt << 1,l,mid#define rson rt << 1 | 1,mid + 1,rconst int maxn = 5e4 + 10;struct Seg {	int l, r, x, cover;	Seg(int x, int l, int r, int cover) :l(l), r(r), x(x), cover(cover) {}	bool operator < (const Seg &seg) const {		return x < seg.x;	}};LL cnt[maxn << 2], len[maxn << 2], n;vector<Seg> seg;void pushup(int rt, int l, int r) {	if (cnt[rt] > 0) len[rt] = r - l + 1;	else if (l == r) len[rt] = 0;	else len[rt] = len[rt << 1] + len[rt << 1 | 1];}void update(int rt, int l, int r, int ql, int qr, int Val) {	if (ql <= l && qr >= r) {		cnt[rt] += Val;		pushup(rt, l, r);	}	else {		int mid = (l + r) >> 1;		if (ql <= mid) update(lson, ql, qr, Val);		if (qr > mid) update(rson, ql, qr, Val);		pushup(rt, l, r);	}}int main() {	int x1, y1, x2, y2, x3, y3, x4, y4, maxval = -1;	while (scanf("%I64d", &n) ,n != 0) {		seg.clear();		memset(cnt, 0, sizeof(cnt));		memset(len, 0, sizeof(len));		for (int i = 1; i <= n; i++) {			scanf("%d%d%d%d%d%d%d%d", &x1, &y1, &x2, &y2, &x3, &y3, &x4, &y4);			seg.push_back(Seg(x1, y1, y2, 1));			seg.push_back(Seg(x3, y1, y2, -1));			seg.push_back(Seg(x4, y1, y2, 1));			seg.push_back(Seg(x2, y1, y2, -1));			seg.push_back(Seg(x3, y1, y3, 1));			seg.push_back(Seg(x4, y1, y3, -1));			seg.push_back(Seg(x3, y4, y2, 1));			seg.push_back(Seg(x4, y4, y2, -1));			maxval = max(maxval, max(max(y1, y2), max(y3, y4)));		}		sort(seg.begin(), seg.end());		int msize = seg.size();		LL ret = 0;		for (int i = 0; i < msize - 1; i++) {			//printf("now is %d %d %d\n", seg[i].l, seg[i].r, seg[i].cover);			if (seg[i].l < seg[i].r) {				update(1, 0, maxval, seg[i].l, seg[i].r - 1, seg[i].cover);			}			ret += (seg[i + 1].x - seg[i].x) * len[1];			//printf("%d add %d\n", i, (seg[i + 1].x - seg[i].x) * len[1]);		}		printf("%I64d\n", ret);	}	return 0;}