Two positive charges of magnitude '$q$' are placed, at the ends of a side (side 1) of a square of side length ‘$2a$’. Two negative charges of the same magnitude are kept at the other corners. Starting from rest, if a charge $Q$ moves from the middle of side 1 to the centre of square, its kinetic energy at the centre of square is $\frac{2kQq}{a}\left(1-\frac{1}{\sqrt{n}}\right)\cdot$The value of $n$ is