from sys import stdin

def fact(n):
	ret = 1
	for i in range(2, n + 1):
		ret *= i
	return ret

def komb(n, k):
	return fact(n) / (fact(k) * fact(n-k))

def skip(a, bit, N, K):
	zbyva = bit_count = a.count(bit)
	index = 0
	while index < N and a[index] == bit:
		index += 1
		zbyva -= 1
	sum = 0
	for i in range(index, N):
		if a[i] == bit:
			zbyva -= 1
			if i >= K - zbyva:
				sum += komb(i, K - zbyva)
	return sum

def soucet_111(a, N):
	same = [True] * N
	ret = []
	pom = False
	for i, bit in zip(range(N-1,-1,-1), a[::-1]):
		ret.insert(0, not(bit ^ pom))
		pom = bit or pom
	ret.insert(0, pom)	
	return ret

def main():
	N, K = [int(i) for i in stdin.readline().strip().split()]
	a = [char == '1' for char in stdin.readline().strip()]
	a_zvetsene = soucet_111(a, N)
	a.reverse()
	a_zvetsene.reverse()
	print((komb(N+1, K) - skip(a, True, N, K) - skip(a_zvetsene, False, N+1, N+1-K)) % 1000000007)

main()