Greedy Algorithm to minimize number of plates used for any array of potholes to cover

Brick roads evidently not being bumpy enough, Little Italy's Mayfield Road has recently developed several potholes. The potholes this year are very bizarre - they are zero-dimensional points which send cars passing over them to a place nobody knows. Unfortunately, the city does not have enough money to hire construction workers, but fortunately, the city does have an enormous reserve supply of 24%24' 2 metal covering plates to prevent cars from entering the underworld. Suppose that you are given an array of the positions of these potholes 3 {81, Sn} where each si represents the distance along the road from the intersection of Euclid and Mayfield to a pothole. Give an algorithm which returns the minimum number of metal plates required to cover all potholes, and prove its correctness. (*)