(LLM-written, always verify, but AC 0.015s)

Bucket passengers by start stop and sweep stops left to right; keep the currently accepted riding passengers in a structure that can return the one with maximum finish stop. When a passenger starts, accept him tentatively; if active accepted count becomes M + 1, delete from the active set the passenger with largest F. This greedy is safe because among simultaneously riding passengers, rejecting the latest-ending one frees capacity earliest for all future events compared with rejecting any earlier-ending one. With buckets plus a max-heap this is O(N + K log K); with a segment tree over finish stops it can be written as O(N + K log N).