Statement

Every February, 10th-grade students at the school select their optional subjects for the next academic year. Each of the N students (numbered from 0 to N - 1) submits a list of subjects they would like to attend. Students must choose at least one and at most five subjects from a total of M available subjects. The subjects are numbered from 1 to M (inclusive). Your task is to help the schedule creator determine which pairs of subjects can be held simultaneously. A pair of subjects (i, j) can be scheduled at the same time if no student has chosen both subjects. Note that the pair (i, j) is considered the same as (j, i).