class Vector2D
{
public:
    double X;
    double Y;

    Vector2D();
    Vector2D(double x, double y);
    Vector2D(const Vector2D &p);
    Vector2D(const Point2D &p1, const Point2D &p2);
    double ScalarProduct(const Vector2D &v);
    bool Collinearity(const Vector2D &v);
    double Length();
    Vector2D& operator= (const Vector2D &v);
};
Vector2D::Vector2D()
{
    X = 0;
    Y = 0;
}
Vector2D::Vector2D(double x, double y)
{
    X = x;
    Y = y;
}
Vector2D::Vector2D(const Vector2D &p)
{
    X = p.X;
    Y = p.Y;
}
Vector2D::Vector2D(const Point2D &p1, const Point2D &p2)
{
    X = p2.X - p1.X;
    Y = p2.Y - p1.Y;
}
istream& operator>>(istream& in, Vector2D &v)
{
    in >> v.X >> v.Y;
    return in;
}
ostream& operator<<(ostream& out, const Vector2D &v)
{
    out << "(" << v.X << ", " << v.Y << ")" << endl;
    return out;
}
Vector2D& Vector2D::operator= (const Vector2D &v)
{

    if (this == &v)
        return *this;
    else
    {
        X = v.X;
        Y = v.Y;
        return *this;
    }
}
double Vector2D::ScalarProduct(const Vector2D &v)
{
    return X * v.X + Y * v.Y;
}
bool Vector2D::Collinearity(const Vector2D &v)
{
    if (X / v.X == Y / v.Y)
        return true;
    else
        return false;
}
double Vector2D::Length()
{
    return sqrt(X * X + Y * Y);
}