#include <iostream>
#include <iomanip>
#include <complex>
#include <vector>
#include <algorithm>
#include <cmath>
#include <array>
#include <map>
#include <queue>
using namespace std;
const double EPS = 1e-10;
const double INF = 1e12;
const double PI = acos(-1);
#define EQ(n,m) (abs((n)-(m)) < EPS)
#define X real()
#define Y imag()

typedef complex<double> P;
typedef vector<P> VP;
struct L : array<P, 2>{
    L(const P& a, const P& b){ at(0)=a; at(1)=b; }
    L(){}
};
namespace std{
    bool operator < (const P& a, const P& b){
        return !EQ(a.X,b.X) ? a.X<b.X : a.Y+EPS<b.Y;
    }
    bool operator == (const P& a, const P& b){
        return abs(a-b) < EPS;
    }
}

double dot(P a, P b){
    return (conj(a)*b).X;
}
double cross(P a, P b){
    return (conj(a)*b).Y;
}
int ccw(P a, P b, P c){
    b -= a;
    c -= a;
    if(cross(b,c) > EPS) return +1; //ccw
    if(cross(b,c) < -EPS) return -1; //cw
    if(dot(b,c) < -EPS) return +2; //c-a-b
    if(abs(c)-abs(b) > EPS) return -2; //a-b-c
    return 0; //a-c-b
}

bool intersectSS(const L& a, const L& b){
    return ( ccw(a[0],a[1],b[0]) *ccw(a[0],a[1],b[1]) <= 0 ) &&
        ( ccw(b[0],b[1],a[0]) *ccw(b[0],b[1],a[1]) <= 0 );
}

bool isParallel(const P &a, const P &b){
    return abs(cross(a,b)) < EPS;
}
bool isParallel(const L &a, const L &b){
    return isParallel(a[1]-a[0], b[1]-b[0]);
}
P crosspointLL(const L &l, const L &m) {
  double A = cross(l[1]-l[0], m[1]-m[0]);
  double B = cross(l[1]-l[0], l[1]-m[0]);
  return m[0] + B/A *(m[1]-m[0]);
}

double getangle(P a, P b){
    return abs(arg(a/b));
}

pair<vector<vector<int> >, VP> arrangement(const vector<L> &l){
    vector<VP> cp(l.size());
    VP plist;
    for(int i=0; i<(int)l.size(); i++){
        for(int j=i+1; j<(int)l.size(); j++){
            if(!isParallel(l[i], l[j]) && intersectSS(l[i], l[j])){
                P cpij = crosspointLL(l[i], l[j]);
                cp[i].push_back(cpij);
                cp[j].push_back(cpij);
                plist.push_back(cpij);
            }
        }
        cp[i].push_back(l[i][0]);
        cp[i].push_back(l[i][1]);
        plist.push_back(l[i][0]);
        plist.push_back(l[i][1]);
        sort(cp[i].begin(), cp[i].end());
        cp[i].erase(unique(cp[i].begin(), cp[i].end()), cp[i].end());
    }
    sort(plist.begin(), plist.end());
    plist.erase(unique(plist.begin(), plist.end()), plist.end());

    int n = plist.size();
    map<P, int> conv;
    for(int i=0; i<n; i++){
        conv[plist[i]] = i;
    }
    vector<vector<int> > adj(n);
    for(int i=0; i<(int)cp.size(); i++){
        for(int j=0; j<(int)cp[i].size()-1; j++){
            int jidx = conv[cp[i][j]];
            int jp1idx = conv[cp[i][j+1]];
            adj[jidx].push_back(jp1idx);
            adj[jp1idx].push_back(jidx);
        }
    }
    for(int i=0; i<n; i++){
        sort(adj[i].begin(), adj[i].end());
        adj[i].erase(unique(adj[i].begin(), adj[i].end()), adj[i].end());
    }
    return make_pair(adj, plist);
}

struct info{
    double d;
    int cidx, pidx;
    info(int p, int c, double d):d(d),cidx(c),pidx(p){}
    info(){}
    bool operator < (const info &a) const{
        return d > a.d;
    }
};

int main(){
    while(1){
        int n;
        cin >> n;
        if(n == 0) break;

        vector<L> l(n);
        for(int i=0; i<n; i++){
            for(int j=0; j<2; j++){
                double x,y;
                cin >> x >> y;
                l[i][j] = P(x,y);
            }
        }
        double sx,sy,gx,gy;
        cin >> sx >> sy >> gx >> gy;
        P s(sx,sy), g(gx,gy);

        pair<vector<vector<int> >, VP> ret = arrangement(l);
        vector<vector<int> > &adj = ret.first;
        VP plist = ret.second;
        int sidx=-1, gidx=-1;
        for(int i=0; i<(int)plist.size(); i++){
            if(plist[i] == s) sidx = i;
            if(plist[i] == g) gidx = i;
        }

        priority_queue<info> wait;
        wait.push(info(-1, sidx, 0));
        vector<vector<double> > mincost(plist.size(), vector<double>(plist.size(), INF));
        double ans = INF;
        while(!wait.empty()){
            int prev = wait.top().pidx;
            int curr = wait.top().cidx;
            double cost = wait.top().d;
            wait.pop();
            if(prev != -1 && cost > mincost[prev][curr] +EPS) continue;
            if(curr == gidx){
                ans = cost;
                break;
            }
            for(int next: adj[curr]){
                double ncost = (prev==-1)? 0: getangle(plist[next] -plist[curr], plist[curr] -plist[prev]);
                if(cost +ncost +EPS < mincost[curr][next]){
                    mincost[curr][next] = cost +ncost;
                    wait.push(info(curr, next, cost +ncost));
                }
            }
        }
        if(ans == INF){
            cout << -1 << endl;
        }else{
            cout << fixed << setprecision(10);
            cout << ans*180/PI << endl;
        }

    }
    return 0;
}


Measured memory_bytes: 3444