A: 안녕하세요. (Hi.)
B: 오랜만이네요. (It's been a long time.)
A: 잘 지내세요? (How are you?)
B: 네. 잘 지내요. (I'm fine.)
A: 네. 다행이네요. 즐거운 하루 보내세요. (Oh, that's good. Have a nice day.)
B: 네. 고마워요! (Okey, thank you!)
In fact, it's a little bit awkward case because many people just say like this:
A: 안녕하세요. (thought: Oh... It's an acquaintance. I don't want to say to any person when I'm alone.)
B: 안녕하세요. (thought: Please don't say to me anymore. I want to be alone this time.)
-The End. Each of them watching their smartphone and just going-
Yep... Hope it helps. :)