K. Microcircuits
time limit per test
2 seconds
memory limit per test
256 megabytes
input
stdin
output
stdout

You probably know how microcircuits look like. First of all it is important to pay special attention to connections. Contacts on the circuit are connected by lines. If two lines do not intersect then there is no connection between respective contacts.

You are holding a circular circuit with n contacts around the borderline. You have to calculate the number of possibilities to put exactly k non-intersecting lines each connecting two contacts.

Input

Single line contains two integers n and k (1 ≤ k ≤ n ≤ 40).

Output

Output the required number.

Examples
Input
4 2
Output
2
Input
4 3
Output
0