#include <bits/stdc++.h>
using namespace std;
#include <atcoder/modint>
using mint = atcoder::modint1000000007;

int main() {
	int N, K;
	cin >> N >> K;
	
	vector<mint> dp(K + 2, 0);
	dp[0] = 1;
	for(int i = 0; i < N; ++i) {
		vector<mint> ndp(K + 2, 0);
		for(int k = 0; k <= K; ++k) {
			ndp[k] += dp[k];
			ndp[min(K + 1, k + i + 1)] -= dp[k];
			ndp[k + 1] += ndp[k];
		}
		swap(dp, ndp);
	}
	
	mint ans = 0;
	for(int k = 0; k <= K; ++k) ans += dp[k];
	cout << ans.val() << "\n";
}