import javax.print.DocFlavor;
import java.io.*;
import java.lang.reflect.Array;
import java.math.BigInteger;
import java.util.*;
import java.util.concurrent.ThreadLocalRandom;

import static java.lang.Math.*;

@SuppressWarnings("Duplicates")

public class solveLOL {
    FastScanner in;
    PrintWriter out;
    boolean systemIO = true, multitests = false;

    lol arr[];
    ArrayList<TreeSet<lol>> mas = new ArrayList<>();
    int mx = 0;

    public void solve() {
        int n = in.nextInt() * 2;
        arr = new lol[n];
        for (int i = 0; i < n; ++i) {
            int x1 = in.nextInt(), y1 = in.nextInt(), x2 = in.nextInt(), y2 = in.nextInt();
            arr[i] = new lol((y1 - y2), (x2 - x1), -((y1 - y2) * x1 + (x2 - x1) * y1));
            int p = gcd(gcd(abs(arr[i].a), abs(arr[i].b)), abs(arr[i].c));
            if (p != 0)
                arr[i] = new lol(arr[i].a / p, arr[i].b / p, arr[i].c / p);
        }
        Arrays.sort(arr, (o1, o2) -> o1.a != o2.a ? Long.compare(o1.a, o2.a) : (o1.b != o2.b) ? Long.compare(o1.b, o2.b) : Long.compare(o1.c, o2.c));
        mas.add(new TreeSet<>((o1, o2) -> o1.a != o2.a ? Long.compare(o1.a, o2.a) : (o1.b != o2.b) ? Long.compare(o1.b, o2.b) : Long.compare(o1.c, o2.c)));
        mas.get(mx).add(arr[0]);
        for (int i = 1; i < n; ++i) {
            if (arr[i].a == arr[i - 1].a && arr[i].b == arr[i - 1].b) {
                mas.get(mx).add(arr[i]);
            } else {
                mx++;
                mas.add(new TreeSet<>((o1, o2) -> o1.a != o2.a ? Long.compare(o1.a, o2.a) : (o1.b != o2.b) ? Long.compare(o1.b, o2.b) : Long.compare(o1.c, o2.c)));
                mas.get(mx).add(arr[i]);
            }
        }
        int k = mas.get(0).first().c;
        for (lol x : mas.get(0)) {
            if (x != mas.get(0).first() && check(x.c - k)) {
                double ans = x.c - k;
                System.out.println(String.format("%8.10f", ans).replace(',', '.'));
                System.exit(0);
            }
        }
        System.out.println("-1.000000000");
    }

    boolean check(int res) {
        for (int i = 0; i < mas.size(); i++) {
            for (lol k : mas.get(i)) {
                if (!mas.get(i).contains(new lol(k.a, k.b, k.c + res)) && !mas.get(i).contains(new lol(k.a, k.b, k.c - res))) {
                    return false;
                }
            }
        }
        return true;
    }
    /*
    3
0 0 0 1
1 0 1 1
2 0 2 1
3 0 3 1
0 0 1 0
0 1 1 1
     */



    class lol {
        int a, b, c;


        lol(int A, int B, int C) {
            this.a = A;
            this.b = B;
            this.c = C;
        }
    }

    int gcd(int a, int b) {
        return b == 1 ? gcd(b, a % b) : a;
    }

    void shuffleArray(long[] ar) {
        Random rnd = ThreadLocalRandom.current();
        for (int i = ar.length - 1; i > 0; i--) {
            int index = rnd.nextInt(i + 1);
            long a = ar[index];
            ar[index] = ar[i];
            ar[i] = a;
        }
    }

    long[] readArray(int size_) {
        long[] ar = new long[size_];
        for (int i = 0; i < size_; i++) {
            ar[i] = in.nextLong();
        }
        return ar;
    }

    void printArray(long[] ar) {
        for (long k : ar) {
            System.out.print(k + " ");
        }
        System.out.println();
    }

    void reverseArray(long[] ar) {
        for (int i = 0, j = ar.length - 1; i < j; i++, j--) {
            long a = ar[i];
            ar[i] = ar[j];
            ar[j] = a;
        }
    }


    class FastScanner {
        BufferedReader br;
        StringTokenizer st;

        FastScanner(File f) {
            try {
                br = new BufferedReader(new FileReader(f));
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            }
        }

        FastScanner(InputStream f) {
            br = new BufferedReader(new InputStreamReader(f));
        }

        String nextLine() {
            try {
                return br.readLine();
            } catch (IOException e) {
                return null;
            }
        }

        String next() {
            while (st == null || !st.hasMoreTokens()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt() {
            return Integer.parseInt(next());
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

    }

    //String.format("%8.3f", ans).replace(',', '.')
    private void run() throws IOException {
        if (systemIO) {
            in = new solveLOL.FastScanner(System.in);
            out = new PrintWriter(System.out);
        } else {
            in = new solveLOL.FastScanner(new File("aplusb.in"));
            out = new PrintWriter(new File("aplusb.out"));
        }
        for (int t = multitests ? in.nextInt() : 1; t-- > 0; )
            solve();

        out.close();
    }

    public static void main(String[] arg) throws IOException {
        new solveLOL().run();
    }

}