N, K = map(int, input().split())
A = input()

if N == 1:
	print(1)
else:
	dp = [[0 for i in range(N * (N - 1))] for j in range(N + 1)]
	dp[1][0] = 1
	j_max = 2
	for i in range(2, N + 1):
		for j in range(max(j_max, K + 1)):
			dp[i][j] = sum(dp[i - 1][max(0, j - i + 1):j + 1])
		j_max += i
	print(sum(dp[N][0:K + 1]) % 1000000007)