A game I won comes with "free copy". Can I give that away?

Several hours ago I won Crash Drive 2 and as you can see in Steam store, when you purchase this game, you also get a free copy to give away. This was a featured giveaway and every single of 450 people who won essentialy got 2 copies of this game.

I wonder making a giveaway for that extra copy would actually be against rules or unethical. After all I would be taking credit for something someone else gave me here, but on the other hand I think giving that extra copy away is better than NOT giving it away. I went through the rules, but this is rather about how it's interpreted, which rules don't seem to target directly.

edit: Thanks for the answers guys! I created the giveaway here, so feel free to join.