Consider the ellipse E given by x²/18 + y²/12 = 1. Let H be the hyperbola whose eccentricity is the reciprocal of the eccentricity of E and whose foci are the same as that of E. Let P and Q be the points of intersection of H and the parabola √5 y = x² in the first quadrant. Let d be the distance between P and Q. If a and b are the integers such that d² = a + b√5, then the value of a − b is ___________.