#include <bits/stdc++.h>

using namespace std;

#define int long long
#define FR first
#define SC second
#define all(v) (v).begin(), (v).end()
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
#define reps(i, f, n) for(int i = (int)(f); i < (int)(n); i++)
#define each(a, b) for(auto& a : b)

typedef pair<int, int> P;

const int inf = 1LL << 55;

#define EPS (1e-10)
#define equals(a, b) (fabs((a)-(b)) < EPS)
#define lt(a, b) ((a) - (b) < -EPS)

// ???/????????????
struct Point {
  double x, y;
  Point(double x = 0.0, double y = 0.0):x(x), y(y){}
  
  Point operator + (Point p) { return Point(x + p.x, y + p.y); }
  Point operator - (Point p) { return Point(x - p.x, y - p.y); }
  Point operator * (double a) { return Point(x * a, y * a); }
  Point operator / (double a) { return Point(x / a, y / a); }

  double abs() { return sqrt(norm()); }
  double norm() { return x*x + y*y; }

  bool operator < (const Point& p) const {
    return x != p.x ? x < p.x : y < p.y;
  }
  bool operator == (const Point& p) const {
    return fabs(x - p.x) < EPS && fabs(y - p.y) < EPS;
  }
};
typedef Point Vector;

// ???
struct Circle {
  Point c;
  double r;
  Circle(Point c = Point(), double r = 0.0):c(c), r(r){}
};

// ????§???¢
typedef vector<Point> Polygon;

// ??????/??´???
struct Segment {
  Point p1, p2;
  Segment(Point p1 = Point(), Point p2 = Point()):p1(p1), p2(p2){}
};
typedef Segment Line;

// ????????????????????????
double norm(Vector v)
{
  return v.x*v.x + v.y*v.y;
}
// ?????????????????§??????
double abs(Vector v)
{
  return sqrt(norm(v));
}
// ?????????????????????
double dot(Vector a, Vector b)
{
  return a.x*b.x + a.y*b.y;
}
// ??????????????????????????§??????
double cross(Vector a, Vector b)
{
  return a.x*b.y - a.y*b.x;
}
// ??´?????????
bool isOrthogonal(Vector a, Vector b)
{
  return equals(dot(a, b), 0.0);
}
bool isOrthogonal(Point a1, Point a2, Point b1, Point b2)
{
  return isOrthogonal(a1 - a2, b1 - b2);
}
bool isOrthogonal(Segment s1, Segment s2)
{
  return equals(dot(s1.p2 - s1.p1, s2.p2 - s2.p1), 0.0);
}
// ????????????
bool isParallel(Vector a, Vector b)
{
  return equals(cross(a, b), 0.0);
}
bool isParallel(Point a1, Point a2, Point b1, Point b2)
{
  return isParallel(a1 - a2, b1 - b2);
}
bool isParallel(Segment s1, Segment s2)
{
  return equals(cross(s1.p2 - s1.p1, s2.p2 - s2.p1), 0.0);
}
// ?°???±
Point project(Segment s, Point p)
{
  Vector base = s.p2 - s.p1;
  double r = dot(p - s.p1, base) / norm(base);
  return s.p1 + base * r;
}
// ????°?
Point reflect(Segment s, Point p)
{
  return p + (project(s, p) - p) * 2.0;
}
static const int COUNTER_CLOCKWISE = 1;
static const int CLOCKWISE         = -1;
static const int ONLINE_BACK       = 2;
static const int ONLINE_FRONT      = -2;
static const int ON_SEGMENT        = 0;
// ???????¨???????
int ccw(Point p0, Point p1, Point p2)
{
  Vector a = p1 - p0;
  Vector b = p2 - p0;
  if(cross(a, b) > EPS) return COUNTER_CLOCKWISE;
  if(cross(a, b) < -EPS) return CLOCKWISE;
  if(dot(a, b) < -EPS) return ONLINE_BACK;
  if(a.norm() < b.norm()) return ONLINE_FRONT;
  return ON_SEGMENT;
}
// ????????????
bool intersect(Point p1, Point p2, Point p3, Point p4)
{
  return (ccw(p1, p2, p3) * ccw(p1, p2, p4) <= 0 &&
	  ccw(p3, p4, p1) * ccw(p3, p4, p2) <= 0);
}
bool intersect(Segment s1, Segment s2)
{
  return intersect(s1.p1, s1.p2, s2.p1, s2.p2);
}
bool intersect(Segment s, Point p)
{
  return (ccw(s.p1, s.p2, p) == ON_SEGMENT);
}
// ?????????????????¢
double getDistance(Point a, Point b)
{
  return abs(a - b);
}
// ??´?????¨?????¨????????¢
double getDistanceLP(Line l, Point p)
{
  return abs(cross(l.p2 - l.p1, p - l.p1) / abs(l.p2 - l.p1));
}
// ????????¨?????¨????????¢
double getDistanceSP(Segment s, Point p)
{
  if(dot(s.p2 - s.p1, p - s.p1) < 0.0) return abs(p - s.p1);
  if(dot(s.p1 - s.p2, p - s.p2) < 0.0) return abs(p - s.p2);
  return getDistanceLP(s, p);
}
// ????????????????????¢
double getDistance(Segment s1, Segment s2)
{
  if(intersect(s1, s2)) return 0.0;
  return min(min(getDistanceSP(s1, s2.p1), getDistanceSP(s1, s2.p2)),
	     min(getDistanceSP(s2, s1.p1), getDistanceSP(s2, s1.p2)));
}
// ???????????????
Point getCrossPoint(Segment s1, Segment s2)
{
  Vector base = s2.p2 - s2.p1;
  double d1 = abs(cross(base, s1.p1 - s2.p1));
  double d2 = abs(cross(base, s1.p2 - s2.p1));
  double t = d1 / (d1 + d2);
  return s1.p1 + (s1.p2 - s1.p1) * t;
}

// ????????????
bool merge_if_able(Segment &s1, Segment s2)
{
  if(abs(cross(s1.p2 - s1.p1, s2.p2 - s2.p1)) > EPS) return false;
  if(ccw(s1.p1, s2.p1, s1.p2) == COUNTER_CLOCKWISE ||
     ccw(s1.p1, s2.p1, s1.p2) == CLOCKWISE) return false;
  if(ccw(s1.p1, s1.p2, s2.p1) == ONLINE_FRONT ||
     ccw(s2.p1, s2.p2, s1.p1) == ONLINE_FRONT) return false;
  s1 = Segment(min(s1.p1, s2.p1), max(s1.p2, s2.p2));
  return true;
}
void merge_segments(vector<Segment>& segs)
{
  for(int i = 0; i < segs.size(); i++) {
    if(segs[i].p2 < segs[i].p1) swap(segs[i].p1, segs[i].p2);
  }
  for(int i = 0; i < segs.size(); i++) {
    for(int j = i+1; j < segs.size(); j++) {
      if(merge_if_able(segs[i], segs[j])) {
	segs[j--] = segs.back(), segs.pop_back();
      }
    }
  }
}
// ????????¢??¬???????????????
typedef vector< vector<int> > Graph;

Graph segment_arrangement(vector<Segment>& segs, vector<Point>& ps)
{
  for(int i = 0; i < segs.size(); i++) {
    ps.push_back(segs[i].p1);
    ps.push_back(segs[i].p2);
    for(int j = i+1; j < segs.size(); j++) {
      if(intersect(segs[i], segs[j])) ps.push_back(getCrossPoint(segs[i], segs[j]));
    }
  }
  sort(ps.begin(), ps.end());
  ps.erase(unique(ps.begin(), ps.end()), ps.end());
  Graph graph(ps.size());
  for(int i = 0; i < segs.size(); i++) {
    vector<int> ls;
    for(int j = 0; j < ps.size(); j++) {
      if(intersect(segs[i], ps[j])) {
	ls.push_back(j);
      }
    }
    sort(ls.begin(), ls.end());
    for(int j = 0; j+1 < ls.size(); j++) {
      int u = ls[j], v = ls[j+1];
      graph[u].push_back(v);
      graph[v].push_back(u);
    }
  }
  return graph;
}

// ???ABC????±???????
double getAngle(Point a, Point b, Point c)
{
  Vector v = b - a, w = c - b;
  double alpha = atan2(v.y, v.x), beta = atan2(w.y, w.x);
  if(alpha > beta) swap(alpha, beta);
  double theta = (beta - alpha) * 180 / M_PI;
  return min(theta, 360 - theta);
}

Graph graph;

double dijkstra(int si, int gi, vector<Point> ps)
{
  vector< vector<double> > mincost(graph.size(), vector<double>(graph.size(),inf));
  // ?????????????????¨??°????????????
  typedef tuple<double, int, int> T;
  priority_queue<T, vector<T>, greater<T> > que;
  for(int to : graph[si]) {
    mincost[to][si] = 0.0;
    que.push(make_tuple(0.0, to, si));
  }  
  while(!que.empty()) {
    double c; int now, prev;
    tie(c, now, prev) = que.top(); que.pop();
    if(now == gi) return c;
    for(int to : graph[now]) {
      double cost = c + getAngle(ps[prev], ps[now], ps[to]);
      if(cost - mincost[to][now] < -EPS) {
	mincost[to][now] = cost;
	que.push(make_tuple(cost, to, now));
      }
    }
  }
  return -1;
}

signed main()
{
  cin.tie(0);
  ios_base::sync_with_stdio(0);
  cout << fixed << setprecision(12);
  int n;
  while(cin >> n, n) {
    vector<Segment> ss(n);
    Point s, g;
    rep(i, n) cin >> ss[i].p1.x >> ss[i].p1.y >> ss[i].p2.x >> ss[i].p2.y;
    cin >> s.x >> s.y >> g.x >> g.y;
    vector<Point> ps;
    merge_segments(ss);
    graph = segment_arrangement(ss, ps);
    int si = -1, gi = -1;
    rep(i, ps.size()) {
      if(ps[i] == s) si = i;
      if(ps[i] == g) gi = i;
    }    
    double ans = dijkstra(si, gi, ps);
    if(ans == -1) cout << -1 << endl;
    else cout << ans << endl;
  }
  return 0;
}

Measured memory_bytes: 3456