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)]
	cum = [[] for _ in range(N + 1)]
	dp[1][0] = 1
	cum[1] = [0, 1, 1]
	j_max = 2
	for i in range(2, N + 1):
		sum_val = 0
		cum[i].append(0)
		for j in range(min(j_max, K + 1)):
			dp[i][j] = cum[i - 1][j + 1] - cum[i - 1][max(0, j - i + 1)]
			sum_val += dp[i][j]
			cum[i].append(sum_val)
		j_max += i
		cum[i] += [sum_val] * i
	print(sum(dp[N][0:K + 1]) % 1000000007)