Given the task definition and input, reply with output. Find the movie name from the given conversation. If the movie name is not found give output as "unknown"

ASSISTANT: What kinds of movies do you typically enjoy? , USER: Mostly, I enjoy action movies and science fiction movies. , ASSISTANT: what draws you to that kind of movie? , ASSISTANT: I see. and what kinds of movies do you tend to dislike or avoid? , USER: I tend to avoid any type of romance movies or movies with a big boring story. , ASSISTANT: Why do you avoid those kinds of movies? , USER: They just don't interest me, I feel like they're boring and they're not fun to watch. They just don't speak to me. , ASSISTANT: I see. So what's a movie you've seen that you really enjoyed? , USER: Oh, boy. , USER: I really like the Back to the Future series, I think that's a great series with a good plot, science fiction, has a great story I have re-watched it many times and I still I can watch it 10 more times and not be bored.
Back to the Future series