Hehe, it doesn't matter. This problem is very common. Maybe others will suddenly forget the name, won't they? Your intention is to say hello to him. It doesn't matter if you don't know the name. Say "Where are you going?" Or "long time no see". There is also a saying called "Have you eaten?" I hate to say this. After greeting, others will know your name.
o(∩_∩)o ...