#!/usr/bin/env pypy3

from pprint import pprint
from string import ascii_lowercase as letter
from sys import setrecursionlimit, stdin
from typing import Dict, Iterable, Set

try:
    import pypyjit

    pypyjit.set_param("max_unroll_recursion=-1")
except ModuleNotFoundError:
    ...

INF: int = (1 << 62) - 1
MOD1000000007 = 10**9 + 7
MOD998244353 = 998244353
setrecursionlimit(500_000)
readline = stdin.readline
input = lambda: stdin.readline().rstrip("\r\n")


def inputs(type_=int):
    ins = input().split()

    if isinstance(type_, Iterable):
        return [t(x) for t, x in zip(type_, ins)]
    else:
        return list(map(type_, ins))


def input_(type_=int):
    (a, ) = inputs(type_)
    return a


def input1() -> int:
    return int(readline())


inputi = input1


def input2():
    a = readline().split()
    assert len(a) == 2
    a[0] = int(a[0])
    a[1] = int(a[1])
    return a


def input3():
    a = readline().split()
    assert len(a) == 3
    a[0] = int(a[0])
    a[1] = int(a[1])
    a[2] = int(a[2])
    return a


def input4():
    a = readline().split()
    assert len(a) == 4
    a[0] = int(a[0])
    a[1] = int(a[1])
    a[2] = int(a[2])
    a[3] = int(a[3])
    return a


# start coding
from typing import List, Optional

n, l = input2()
mod = MOD1000000007

if n < l:
    # print(pow(2, n - 1, mod))
    print(pow(2, n - 1))
    exit()

a = [None] * (n + 1)
a[0] = 1
for i in range(1, l):
    a[i] = pow(2, i - 1, mod)

s = 0
for i in range(l):
    s += a[i]
    s %= mod

for i in range(l, n + 1):
    a[i] = sum(a[i - l:i])
    a[i] %= mod

# print(a)
print(a[-1])