MOD = 10 ** 9 + 7

n, l = map(int, input().split())
dp = [0] * (n + 1)
dp[0] = 1
cum = [0] * (n + 1)
cum[0] = 1

for i in range(1, n + 1):
    dp[i] = cum[i - 1]
    if i - l >= 1:
        dp[i] -= cum[i - l - 1]
    dp[i] %= MOD
    cum[i] = cum[i - 1] + dp[i]
    cum[i] %= MOD
print(dp[-1])