How do you stop other person's legs contact my legs in a bus?

Day before yesterday i had to sit on a middle seat in the bus between the window and another seat where somebody was sitting, i m a male of 17). But when i sat after sometime i felt like my leg contacts with other persons. so i mover mine towards me a little bit. Then again i felt like contacting. so i tried to stop that. then i realised as other person was doing it himself. in this case i felt very uncomfortable. So is this a common situation and what do in these situation?