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

DP=[0]*(N+L+5)
DP[0]=1

for i in range(N):
    DP[i]+=DP[i-1]
    DP[i]%=mod
    x=DP[i]
    DP[i+1]+=x
    DP[i+L+1]-=x

print(DP[N]%mod)