Because of a recent wave of jewellery store robberies, a city increases police surveillance of jewellery stores. The increased surveillance costs the city an extra $500,000 per year, but as a result, the amount of jewellery that is stolen falls. Specifically, without the increase in surveillance, jewellery with a retail value of $900,000 would have been stolen. This stolen jewellery would have been fenced by the jewellery thieves for $600,000. What is the net social benefit resulting from the police surveillance program?