The following are the starting and ending times of activities A, B, C, D, E, F, G and H respectively in chronological order: “as bs cs ae ds ce es fs be de gs ee fe hs ge he”. Here, xs denotes the starting time and xe denotes the ending time of activity X. We need to schedule the activities in a set of rooms available to us. An activity can be scheduled in a room only if the room is reserved for the activity for its entire duration. What is the minimum number of rooms required?