I don’t mind people saying hello, but also would prefer they then go ahead and state their need. I don’t always respond right away, and often times by the time I get around to answering the need is gone or the person is unavailable. I definitely don’t mind interrupting my work flow, especially to route somebody to the actual correct person who can help them with their problem, but I don’t like the expectation of a synchronous conversation, so a “hello” with nothing else will usually fall to the bottom of my list of actual concrete problems to address for that minute/hour/day.