I have a stationary bike that I do twice a week, but I'm not...

I have a stationary bike that I do twice a week, but I'm not really serious about it. I just do it until I get tired. And then I have a step thing that I really hate. It's hard on your knees. I have a treadmill that keeps getting stuck. It's nice to have equipment around, though, because you can sit on it anytime.