How do I know what generation my iPod Shuffle is?

Just got this little guy on Monday…and lovin’ it. So, I was browsing for a wall charger (to free up my PC port) and discovered that I need to know whether it’s 1st, 2nd, or 3rd generation. I’ve looked through the stuff that came with it…and no luck. How do I know? I’ve got no clue about this – it’s probably obvious and I’ll feel like an idiot, I’m sure. Help!