01 Sequence 2

Problem Description

Here comes everyone's favorite 01-sequence problem again.

This time the problem is very simple. cc thinks that in a 01 sequence there should be at least $k$ zeros between any two $1$s. Now he wants to construct a 01 sequence of length $n$. How many different construction methods are there?

This number may be very large, so please output it modulo $10^9 + 7$.

Input Format

A single line containing two integers $n, k$.

Output Format

One integer: the number of different construction methods.

Sample Input

4 2

Sample Output

6

Constraints

$1 \le n \le 10^6$

$0 \le k < n$