Science, maths and just a little bit of chocolate

You know that theory that if you eat a stick of celery you actaully burn more calories chewing it than you gain from the nutritionally-challenged vegetable itself?
Well, I have developed my own, slightly more indulgent version of this, involving a hell of a lot more sugar and fat... and pleasure.
I live on the third floor of an old building, which therefore has no lift. My reasoning is that by descending three flights of stairs, speed-walking to the bakery at the end of the street, and dashing back up to the flat, I have actually burned more calories than I will gain from whatever cream-filled and chocolate-coated piece of yumminess I choose to buy from the bakery.
This means that, in theory, this activity could be repeated endlessly throughout the day, with no increase in calories whatsoever, and a damn good pair of thighs at the end of it.
Isn´t that the perfect solution to winter blues?!