In mountainous areas, reception of radio and television is sometimes poor. Consider an idealized case where a hill is represented by the graph of the parabola y = x - x, a transmitter is located at the point (-3, 3), and a receiver is located on the other side of the hill at the point (x, 0). What is the closest the receiver can be to the hill while still maintaining unobstructed reception? (Round your answer to three decimal places.)