#include <iostream>
#include <complex>
#include <random>
#include <cstdlib>
#include <deque>
#include <algorithm>

using namespace std;

const int mod = 1e9 + 7;
int dp[5005][5005][2];
int dp2[5005][5005][2];

void add(int &a, int b) {
	long long c = a;
	c += (long long)b;
	c %= mod;
	a = c;
}

signed main()
{
	int n, k;
	cin >> n >> k;
	if (n == k) {
		cout << 1;
		exit(0);
	}
	dp[k][k][1] = dp[k][k][0] = 1;
	for (int i = 1; i <= n; ++i)
	{
		if (i >= k) {
			dp2[k][i][0] = dp2[k][i][1] = 1;
		}
	}
	for (int sum = k + 1; sum <= n; ++sum)
	{
		for (int last = 1; last <= sum; ++last) {
			add(dp[sum][last][0], dp2[sum - last][last - 1][1]);
			int f = dp2[sum - last][sum][0] - dp2[sum - last][last][0];
			if (f < 0) f += mod;
			f %= mod;
			add(dp[sum][last][1], f);
		}
		int sm0 = 0;
		int sm1 = 0;
		for (int i = 1; i <= n; ++i) {
			add(sm0, dp[sum][i][0]);
			add(sm1, dp[sum][i][1]);
			dp2[sum][i][0] = sm0;
			dp2[sum][i][1] = sm1;
		}
	}
	int ans = 0;
	for (int last = 1; last <= n; ++last) {
		add(ans, dp[n][last][0]);
		add(ans, dp[n][last][1]);
	}
	cout << ans;
	return 0;
}