N, L = map(int, input().split())
MOD = 10**9 + 7

fib = [0] * (N + 1)
AAC = [0]
fib[0] = 1
AAC.append(1)
for i in range(1, N + 1):
    # fib[i] = sum(fib[max(0, i - L):i]) % MOD
    fib[i] = AAC[-1] - AAC[max(0, i - L)]
    fib[i] %= MOD
    AAC.append(AAC[-1] + fib[i])
    AAC[-1] %= MOD

print(fib[-1])