#include <bits/stdc++.h>
using namespace std;

int main()
{
	int64_t N, L;
	cin >> N >> L;
	const int64_t mod = 1000000007;
	
	vector<int64_t> dp(N + 1);
	dp[0] = 1;
	int64_t S = 1;
	int64_t count = 1;
	for(int64_t i = 1; i <= N; i++)
	{
		if(count != L)
		{
			dp[i] = S;
			S += dp[i];
			S %= mod;
			count++;
		}
		else
		{
			dp[i] = S;
			S += dp[i];
			S -= dp[i - L];
			S += mod;
			S %= mod;
		}
	}
	
	cout << dp[N] << endl;
	return 0;
}