I'm a bit confused about the usage of full names and short names (I'm not sure if this is the right way to call them, what I mean is for example Александр vs. Саша). When would you introduce yourself with your full name, and when with your short name? And if someone introduced himself/herself with his/her full name, would it be considered impolite if you use the short name? When do you switch from one to the other?
It would be great if someone could shed some light on this...