import sys; input = sys.stdin.buffer.readline
sys.setrecursionlimit(10**7)
from collections import defaultdict
con = 10 ** 9 + 7; INF = float("inf")

def getlist():
	return list(map(int, input().split()))

#処理内容
def main():
	N, K = getlist()
	DP = [0] * (N ** 2 + N + 1)
	DP[0] = 1
	for i in range(1, N):
		DPs = [0] * (N ** 2 + N + 2)
		for j in range(1, N ** 2 + N + 2):
			DPs[j] = (DPs[j - 1] + DP[j - 1]) % con
		# print(DPs)
		for j in range(N ** 2 + N, -1, -1):
			if j - i >= 0:
				DP[j] = DPs[j + 1] - DPs[j - i]
			else:
				DP[j] = DPs[j + 1]
		# print(DP)

	# print(DP)
	ans = 0
	for i in range(K + 1):
		ans += DP[i]
		ans %= con

	print(ans)
	




if __name__ == '__main__':
	main()