Merry decided fireflies illuminate the world with its soft light, but can not do this in spite of the large number of individuals. However, his idea, they did not let go and decided to light a bright bulb. Your task is to help these flying insects cope with the lighting. Come up with a logical move, with which you can pick up a heavy wooden shelf and get to the bulb. As soon as the luminous device will be in the legs flock of fireflies, they will be able to screw it in and then the entries will be light.