How to put ads on an wordpress.COM blog?

For those who don’t know, WordPress.COM lets you make your on blog and they host it for you. Simple stuff.
Wordpress.ORG gives you the files so you can host your own blog
Can I put ad’s (any kind, I dont care) on my wordpress.COM blog? All my content is there and I don’t want to switch hosts just to put some ads on there.
Many thanks.

Original post by henryhavoc