Nuclear Power Station

Time Limit: 1000 mSec

Memory Limit: 32768 KB

Description

A nuclear power station has N special containers lined up, which is used to store radioactive material. The material can destroy the whole station if they are placed into M consecutive containers. Therefore, some containers have to be left empty.

Given N,M, your task is to calculate the number of safe placement.

Input

There are multiple test cases. Each case contains only one line containing two integers, N and M (1<N<50, 2<=M<=5)
Process to the end of file.

Output

For each case, output a integer representing the number of safe placement.

Sample Input

4 3

Sample Output

13

Hint

Source


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