You're given a list of time intervals during which students at a school need a laptop. These time intervals are represented by pairs of integers [start, end], where 0 <= start < end. However, start and end don't represent real times; therefore, they may be greater than 24. No two students can use a laptop at the same time, but immediately after a student is done using a laptop, another student can use that same laptop. For example, if one student rents a laptop during the time interval [0, 2], another student can rent the same laptop during any time interval starting with 2. Write a function that returns the minimum number of laptops that the school needs to rent such that all students will always have access to a laptop when they need one.