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#include <bits/stdc++.h>
#define mk std::make_pair
#define st first
#define nd second
#define ld long double
#define debug if(0)

struct Point{
    ld x, y;
    Point(ld x, ld y){
        this->x = x; this->y = y;
    }
    Point(){
        x = 0; y = 0;
    }
};

std::vector<Point> Z;
std::vector<std::pair<Point, Point> > E;
std::vector<Point> P;
int n;

void input(){
    std::cin >> n;
    ld ax, ay, bx, by;
    for (int i = 1; i <= n; i++){
        std::cin >> ax >> ay >> bx >> by;
        Point A(ax, ay);
        Point B(bx, by);
        E.push_back(mk(A, B));
        Z.push_back(A); Z.push_back(B);
    }
}

////////////// TUTAJ SA WSZYSTKIE FUNKCJE UTILITY  ////////////////////////

ld distance(const Point &p1, const Point &p2){
    return (p1.x - p2.x)*(p1.x - p2.x) + (p1.y - p2.y)*(p1.y - p2.y);
}

ld det(Point p1, Point p2, Point p3){
    ld D = p1.x*p2.y + p3.x*p1.y + p2.x*p3.y - p2.x*p1.y - p1.x*p3.y - p3.x*p2.y;
    return D;
}

ld triangleArea(Point &p1, Point &p2, Point &p3){
    ld area = det(p1, p2, p3);
    if (area < 0)
        area *= (ld)(-1);
    area /= (ld)(2);
    return area;
}

ld polygonArea(std::vector<Point> &v){
    if (v.size() <= 2)
        return (ld)(0);
    ld area = 0;
    for (int i = 1; i <= v.size()-3; i++)
        area += triangleArea(v[0], v[i], v[i+1]);
    return area;
}

Point pointOfIntersection(Point &U, Point &V, Point &X, Point &Y){
    // punkt przeciecia odcinka X --> Y z prostą wyznaczona przez punkty U i V (wiem ze sie przecinaja, sprawdzilem wczesniej)
    if (U.x == V.x){
        // plaszczyzna wyznaczona jest przez linie pionowa
        ld c = (X.y - Y.y)/(X.x - Y.x);
        ld d = (X.x*Y.y - Y.x*X.y)/(X.x-Y.x);
        ld x = U.x;
        ld y = c*x+d;
        Point H(x, y);
        return H;
    }
    else if (X.x == Y.x){
        // odcinek jest pionowy
        ld a = (U.y - V.y)/(U.x - V.x);
        ld b = (U.x*V.y - V.x*U.y)/(U.x-V.x);
        ld x = X.x;
        ld y = a*x+b;
        Point H(x, y);
        return H;
    }
    else{
        // nic nie jest pionowe
        ld a = (U.y - V.y)/(U.x - V.x);
        ld b = (U.x*V.y - V.x*U.y)/(U.x-V.x);
        ld c = (X.y - Y.y)/(X.x - Y.x);
        ld d = (X.x*Y.y - Y.x*X.y)/(X.x-Y.x);
        ld x = (d-b)/(a-c);
        ld y = a*x+b;
        Point H(x, y);
        return H;
    }
}

///////////////////////////////////////////////////////////////////////////

bool exists(Point &U, Point &V){
    // zwraca true wtedy i tylko wtedy gdy po prawej stronie znajduje sie jakis odcinkek
    for (auto p: E){
        ld d1 = det(U, V, p.st);
        ld d2 = det(U, V, p.nd);
        if (d1 < 0 && d2 < 0)
            return true;
    }
    return false;
}

void findIntersection(Point &U, Point &V){
    // polplaszczyzna wyznaczona przez wektor U --> V, chce zrobic czesc wspolna z jej lewą stroną
    if (P.empty())
        return;
    std::vector<Point> tmp;
    for (int i = 0; i < P.size()-1; i++){
        Point X = P[i];
        Point Y = P[i+1];
        ld dt = det(U, V, X);
        ld dh = det(U, V, Y);

        if (dt <= 0.0000000001 && dt >= -0.0000000001)
            dt = 0;
        if (dh <= 0.0000000001 && dh >= -0.0000000001)
            dh = 0;

        if (dt < 0 && dh > 0){
            // wchodzi
            Point H = pointOfIntersection(U, V, X, Y);
            tmp.push_back(H);
            tmp.push_back(Y);
        }
        else if (dt > 0 && dh < 0){
            // wychodzi
            Point H = pointOfIntersection(U, V, X, Y);
            tmp.push_back(H);
        }
        else if (dt > 0 && dh > 0){
            // 1
            tmp.push_back(Y);
        }
        else if (dt < 0 && dh < 0){
            // 2
            continue;
        }
        else if (dt == 0 && dh == 0){
            // 1
            tmp.push_back(Y);
        }
        else if (dt < 0 && dh == 0){
            // 1t
            tmp.push_back(Y);
        }
        else if (dt == 0 && dh > 0){
            // 1
            tmp.push_back(Y);
        }
        else if (dt > 0 && dh == 0){
            // 1
            tmp.push_back(Y);
        }
        else if (dt == 0 && dh < 0){
            // 2
            continue;
        }
    }
    P = tmp;
    if (P.size() > 0)
        P.push_back(P.front());
}

void findArea(){
    for (int i = 0; i < Z.size(); i++){
        for (int j = 0; j < Z.size(); j++){
            if (i == j)
                continue;
            if (!exists(Z[i], Z[j]))
                findIntersection(Z[i], Z[j]);
        }
    }
}

int main(){
    std::ios_base::sync_with_stdio(0); std::cin.tie(NULL);
    input();
    P.emplace_back(-500, -500);
    P.emplace_back(500, -500);
    P.emplace_back(500, 500);
    P.emplace_back(-500, 500);
    P.emplace_back(-500, -500);
    findArea();

    ld area = polygonArea(P);
    std::cout << std::setprecision(16) << std::fixed << area << "\n";
}