We consider the square whose vertices have coordinates (2, 2), (2, 2), (2, 2), (2, 2) and put a barrier on the border of that square. A walker start at the point (1;0) an takes steps of distance 1 by choosing each time left,right, up or down at random and taking one step in that direction. We call X the number of steps the walker makes until they hit the barrier. 

Give a closed formula for P (X = n). (Please use generating function approach)