Grammy bought a big cake. The shape of the cake is a regular polygon. That is, a convex polygon whose all interior angles are equal and all edges are equal.

Grammy wants to cut the cake into a pretty pattern and share the cake with her friends. She indexed the vertices through in counterclockwise order and chooses an integer . After that, she cuts the cake through straight lines connecting vertex and vertex for each .

Grammy wants to know the number of pieces after cutting the cake. Please calculate it for her.

The only line contains  integers  (), denoting the number of sides of the regular polygon and the integer chosen by Grammy.

Output a single integer in a line, denoting the number of pieces after cutting the cake.

6 2

13

For the sample test case, the final cake is shown below: