SuperBijeg

Slavko found out that Mirko was digging around in his room again! Slavko is really mad this time and wants to catch Mirko. But this time, Mirko is not even safe in his own house! Since Slavko is a lazy person, he will give up if Mirko runs too far away.

Imagine that Mirko is running away on a plane. Slavko's house is located in the centre, point with coordinates (0,0), and that is actually Mirko's starting position. Slavko will give up if Mirko gets to the point (n, n).

Mirko doesn't want to go back towards Slavko's house. At every moment he moves in one of the two directions: if he is at the point (x,y), he can move to the point (x+1, y) or (x, y+1) - up or right.

Also, Mirko can't get to the point (x, y) where x < y, because he could fall in the holes that Slavko dug on that part of his property.

Being an excellent mathematician, Mirko noticed that there can exist different paths to the point (n,n).

While he is running away, you have to write a program that calculates the number of different paths to the point (n,n).