#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <climits>
#include <cassert>
#include <iostream>
#include <iomanip>
#include <sstream>
#include <algorithm>
#include <numeric>
#include <complex>
#include <stack>
#include <queue>
#include <list>
#include <set>
#include <map>
#include <bitset>
#include <functional>
#include <iterator>

using namespace std;

#define dump(n) cout<<"# "<<#n<<'='<<(n)<<endl
#define repi(i,a,b) for(int i=int(a);i<int(b);i++)
#define peri(i,a,b) for(int i=int(b);i-->int(a);)
#define rep(i,n) repi(i,0,n)
#define per(i,n) peri(i,0,n)
#define iter(c) __typeof__((c).begin())
#define foreach(i,c) for(iter(c) i=(c).begin();i!=(c).end();++i)
#define all(c) (c).begin(),(c).end()
#define mp make_pair

typedef unsigned int uint;
typedef long long ll;
typedef unsigned long long ull;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<double> vd;
typedef vector<vd> vvd;
typedef vector<string> vs;
typedef pair<int,int> pii;

const int INFTY=1<<29;
const double EPS=1e-9;

template<typename T1,typename T2>
ostream& operator<<(ostream& os,const pair<T1,T2>& p){
	return os<<'('<<p.first<<','<<p.second<<')';
}
template<typename T>
ostream& operator<<(ostream& os,const vector<T>& a){
	os<<'[';
	rep(i,a.size()) os<<(i?" ":"")<<a[i];
	return os<<']';
}

const double PI=acos(-1);

struct Point{
	double x,y;
	Point(){}
	Point(double x,double y):x(x),y(y){}
};
struct Line{
	Point pos,dir;
	Line(){}
	Line(Point p,Point d):pos(p),dir(d){}
	Line(double px,double py,double dx,double dy):pos(px,py),dir(dx,dy){}
};
typedef Line Segment;

bool operator==(Point a,Point b){
	return abs(a.x-b.x)<EPS && abs(a.y-b.y)<EPS;
}
bool operator!=(Point a,Point b){
	return !(a==b);
}
Point operator+(Point a,Point b){
	return Point(a.x+b.x,a.y+b.y);
}
Point operator-(Point a,Point b){
	return Point(a.x-b.x,a.y-b.y);
}
Point operator*(double c,Point p){
	return Point(c*p.x,c*p.y);
}
Point operator/(Point p,double c){
	return Point(p.x/c,p.y/c);
}
struct LessX{
	bool operator()(Point a,Point b){
		return abs(a.x-b.x)>EPS?a.x<b.x-EPS:a.y<b.y-EPS;
	}
};

int Signum(double x){
	return x<-EPS?-1:x<EPS?0:1;
}
double Abs(Point p){
	return sqrt(p.x*p.x+p.y*p.y);
}
double Abs2(Point p){
	return p.x*p.x+p.y*p.y;
}
double Arg(Point p){
	return atan2(p.y,p.x);
}
double Dot(Point a,Point b){
	return a.x*b.x+a.y*b.y;
}
double Cross(Point a,Point b){
	return a.x*b.y-a.y*b.x;
}
int CCW(Point a,Point b,Point c){
	Point d1=b-a,d2=c-a;
	if(int sign=Signum(Cross(d1,d2)))
		return sign;	// 1:ccw,-1:cw
	if(Dot(d1,d2)<-EPS)
		return -2;		// c-a-b
	if(Abs2(d1)<Abs2(d2)-EPS)
		return 2;		// a-b-c
	return 0;			// a-c-b
}

bool IntersectSP(Segment s,Point p){
	return CCW(s.pos,s.pos+s.dir,p)==0;
}
bool IntersectSS(Segment a,Segment b){
	int c1=CCW(a.pos,a.pos+a.dir,b.pos),c2=CCW(a.pos,a.pos+a.dir,b.pos+b.dir);
	int c3=CCW(b.pos,b.pos+b.dir,a.pos),c4=CCW(b.pos,b.pos+b.dir,a.pos+a.dir);
	return c1*c2<=0 && c3*c4<=0;
}
Point InterPointLL(Line a,Line b){
	if(abs(Cross(a.dir,b.dir))<EPS)
		return a.pos;
	return a.pos+Cross(b.pos-a.pos,b.dir)/Cross(a.dir,b.dir)*a.dir;
}
Point InterPointSS(Segment a,Segment b){
	if(abs(Cross(a.dir,b.dir))<EPS){
		if(IntersectSP(b,a.pos)) return a.pos;
		if(IntersectSP(b,a.pos+a.dir)) return a.pos+a.dir;
		if(IntersectSP(a,b.pos)) return b.pos;
		if(IntersectSP(a,b.pos+b.dir)) return b.pos+b.dir;
	}
	return InterPointLL(a,b);
}

struct Edge{
	int src,dst;
	double weight;
	Edge(){}
	Edge(int s,int d,double w):src(s),dst(d),weight(w){}
	bool operator<(const Edge& e)const{return Signum(weight-e.weight)<0;}
	bool operator>(const Edge& e)const{return Signum(weight-e.weight)>0;}
};
typedef vector<vector<Edge> > Graph;

void SegmentArrangement(const vector<Segment>& ss,Graph& g,vector<Point>& ps){
	rep(i,ss.size()){
		ps.push_back(ss[i].pos);
		ps.push_back(ss[i].pos+ss[i].dir);
		repi(j,i+1,ss.size()) if(IntersectSS(ss[i],ss[j]))
			ps.push_back(InterPointSS(ss[i],ss[j]));
	}
	sort(all(ps),LessX());
	ps.erase(unique(all(ps)),ps.end());
	
	g.resize(ps.size());
	rep(i,ss.size()){
		vector<pair<double,int> > ds;
		rep(j,ps.size()) if(IntersectSP(ss[i],ps[j]))
			ds.push_back(mp(Abs(ps[j]-ss[i].pos),j));
		sort(all(ds));
		rep(j,ds.size()-1){
			int u=ds[j].second,v=ds[j+1].second;
			double w=ds[j+1].first-ds[j].first;
			g[u].push_back(Edge(u,v,w));
			g[v].push_back(Edge(v,u,w));
		}
	}
}

int main()
{
	for(int n;cin>>n,n;){
		vector<Segment> ss(n);
		rep(i,n){
			int x1,y1,x2,y2; cin>>x1>>y1>>x2>>y2;
			ss[i]=Segment(x1,y1,x2-x1,y2-y1);
		}
		Point st,go;
		cin>>st.x>>st.y>>go.x>>go.y;
		
		Graph g;
		vector<Point> ps;
		SegmentArrangement(ss,g,ps);
		
		vi sum(g.size());
		repi(i,1,g.size())
			sum[i]=sum[i-1]+g[i-1].size();
		
		Graph g2(sum.back()+g.back().size());
		rep(i,g.size()) rep(j,g[i].size()) rep(k,g[g[i][j].dst].size()){
			Edge e1=g[i][j],e2=g[g[i][j].dst][k];
			int u=sum[e1.src]+j,v=sum[e2.src]+k;
			double w=abs(Arg(ps[e1.dst]-ps[e1.src])-Arg(ps[e2.dst]-ps[e2.src]))*180/PI;
			w=min(w,360-w);
			g2[u].emplace_back(u,v,w);
		}
		
		vi sts,gos;
		rep(i,g.size()) rep(j,g[i].size()){
			Segment seg(ps[i],ps[g[i][j].dst]-ps[i]);
			if(IntersectSP(seg,st)) sts.push_back(sum[i]+j);
			if(IntersectSP(seg,go)) gos.push_back(sum[i]+j);
		}
		
		vd ws(g2.size(),INFTY);
		priority_queue<Edge,vector<Edge>,greater<Edge>> pq;
		rep(i,sts.size()) pq.emplace(-1,sts[i],0);
		while(!pq.empty()){
			Edge cur=pq.top(); pq.pop();
			if(ws[cur.dst]!=INFTY) continue;
			ws[cur.dst]=cur.weight;
			for(Edge e:g2[cur.dst])
				pq.emplace(e.src,e.dst,cur.weight+e.weight);
		}
		double res=INFTY;
		rep(i,gos.size()) res=min(res,ws[gos[i]]);
		
		if(res==INFTY) puts("-1");
		else           printf("%f\n",res);
	}
	
	return 0;
}

Measured memory_bytes: 1364