def cross_product(vec1, vec2):
    """
    Do cross product with two vector.
    @param { Vector2 } vec1 : first vector.
    @param { Vector2 } vec2 : second vector.
    @return { float } : Return the scalar.
    """

    return vec1.get_x() * vec2.get_y() - vec1.get_y() * vec2.get_x()