For the four circles M, N, O and P, following four equations are given :Circle M : x² + y² = 1, Circle N : x² + y² $-$ 2x = 0 ,Circle O : x² + y² $-$ 2x $-$ 2y + 1 = 0, Circle P : x² + y² $-$ 2y = 0

If the centre of circle M is joined with centre of the circle N, further center of circle N is joined with centre of the circle O, centre of circle O is joined with the centre of circle P and lastly, centre of circle P is joined with centre of circle M, then these lines form the sides of a :