N, L = map(int, input().split())
dp = [0]*(N+1)
dp[0] = 1
acc = 1
MOD = 10**9+7

for i in range(1, N+1):
    dp[i] = acc
    acc += dp[i]
    acc %= MOD
    
    if i>=L:
        acc -= dp[i-L]
        acc %= MOD

print(dp[N])