n, l = input().split()
n = int(n)
l = int(l)
mod = 1000000007

if n < l:
    print(pow(2, n - 1, mod))
    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] = s
    s -= a[i - l]
    s += a[i]
    s %= mod

print(a[n])