How do you do the magic number trick in one second?

Perform the trick:

1. Think of a number, any positive integer. Keep it small so you can do computations in your head.
2. Square it.
3. Add the result to your original number.
4. Divide by your original number.
5. Add, oh, how about 17.
6. Subtract your original number.
7. Divide by 6.
8. The number you are thinking of now is 3!