Three small identical neutral metal balls are at the vertices of an equilateral triangle. The balls are in turn touched to an isolated large charged conducting sphere whose centre is on a line perpendicular to the plane of triangle and passing through its centre. As a result the first and second balls have acquired charges $$q_1$$ and $$q_2$$ respectively. The charge acquired by the third ball is [Assume that charge and potential of large spherical conductor change insignificantly in charging of the balls and that charges on balls are spherically symmetric]