N, L = gets.split.map(&:to_i)
MOD = 10 ** 9 + 7

dp = Array.new(N + 1, 0)
dp[0] = 1
sum = 1

1.upto(N) do |i|
  dp[i] = sum
  dp[i] %= MOD
  sum += dp[i]
  sum -= dp[i - L] if i - L >= 0
  sum %= MOD
end

puts dp[N]