l, h = [int(i) for i in input().split()]
b = list (map (int, input().split()))

f = [[0 for i in range (99)] for j in range (99)]
f[0][0] = 1
for n in range (l + 1):
	for k in range (90):
		if k < b[n]:
			f[n][k] = 0
		f[n + 1][k + 1] += f[n][k]
		f[n + 1][k + 2] += f[n][k]

print (f[l][h])