Bijeg

Slavko found out that Mirko was digging around in his room so he is acting that he is mad to make Mirko run 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. Mirko wants to get to his house, which is located at the point (A, B).

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 his home.

While he is running home, you have to write a program that calculates the number of different paths to Mirko's house. If Mirko can't get to his house, then the number of paths is 0.