An exhibition of the work of a modern artist is currently on display at an art gallery for a period of 30 days. One of the exhibits, entitled “Countdown”, started off as 30 individual identical cylinders arranged in 10 stacks of 3, with the following appearance when viewed from above. Each day since the exhibition began, one cylinder has been removed, and this will continue until there is just one left on day 30. Today is day 11, so 20 cylinders remain. The view from above is still the same as it was on day 1, but the side view today from the direction marked X is: