### BUGGY CODE ###

import sys
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
sys.setrecursionlimit(10 ** 9)
INF = float('inf')
MOD = 10 ** 9 + 7

N, K = LIST()
S = input()

stand = []
reverse = []
state = None
count = 0
tmp = None
for i in S:
	if i == "0":
		state = "stand"
	else:
		state = "reverse"
	if tmp == "stand" and state == "reverse":
		stand.append(count)
		count = 1
	elif tmp == "reverse" and state == "stand":
		reverse.append(count)
		count = 1
	else: # 状態が前と同じ
		count += 1
	tmp = state
if state == "stand":
	stand.append(count)
else:
	reverse.append(count)

if "0" not in S:
	print(len(S))
else:
	if K >= len(stand): # 全員逆立ちにできる
		print(len(S))
	else:
		if len(stand) > len(reverse):
			reverse.append(0)
			reverse.insert(0, 0)
		if len(stand) == len(reverse) and S[0] == "0":
			reverse.insert(0, 0)
		if len(stand) == len(reverse) and S[0] == "1":
			reverse.append(0)
		# print(stand)
		# print(reverse)
		max_ = 0
		for i in range(max(1, 1+len(reverse)-(K+1))):
			# print(reverse[i:i+K+1],stand[i:i+K])
			tmp = sum(reverse[i:i+K+1]+stand[i:i+K])
			if tmp > max_:
				max_ = tmp
		print(max_)

### FIXED CODE ###

import sys
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
sys.setrecursionlimit(10 ** 9)
INF = float('inf')
MOD = 10 ** 9 + 7

N, K = LIST()
S = input()

# stand = []
# reverse = []
# state = None
# count = 0
# tmp = None
# for i in S:
# 	if i == "0":
# 		state = "stand"
# 	else:
# 		state = "reverse"
# 	if tmp == "stand" and state == "reverse":
# 		stand.append(count)
# 		count = 1
# 	elif tmp == "reverse" and state == "stand":
# 		reverse.append(count)
# 		count = 1
# 	else: # 状態が前と同じ
# 		count += 1
# 	tmp = state
# if state == "stand":
# 	stand.append(count)
# else:
# 	reverse.append(count)

# if "0" not in S:
# 	print(len(S))
# else:
# 	if K >= len(stand): # 全員逆立ちにできる
# 		print(len(S))
# 	else:
# 		if len(stand) > len(reverse):
# 			reverse.append(0)
# 			reverse.insert(0, 0)
# 		if len(stand) == len(reverse) and S[0] == "0":
# 			reverse.insert(0, 0)
# 		if len(stand) == len(reverse) and S[0] == "1":
# 			reverse.append(0)
# 		# print(stand)
# 		# print(reverse)
# 		max_ = 0
# 		for i in range(max(1, 1+len(reverse)-(K+1))):
# 			# print(reverse[i:i+K+1],stand[i:i+K])
# 			tmp = sum(reverse[i:i+K+1]+stand[i:i+K])
# 			if tmp > max_:
# 				max_ = tmp
# 		print(max_)
indexes = [0]
if S[0] == "0":
    indexes.append(0)
for i in range(N-1):
	if S[i] != S[i+1]:
		indexes.append(i+1)
indexes.append(N)
if S[N-1] == "0":
    indexes.append(N)
ans = []
# print(indexes)
r = len(indexes)//2 -1
if K >= r:
	print(N)
else:
	print(max(indexes[2*(i+K)+1]-indexes[2*i] for i in range(r-K+1)))
	# for i in range(len(indexes)):
	# 	# print(i)
	# 	if i == len(indexes)-1:
	# 		break
	# 	if S[indexes[i]] == "0":
	# 		if i+2*K >= len(indexes):
	# 			continue
	# 		ans.append(indexes[i+2*K]-indexes[i])
	# 	else:
	# 		if i+2*K+1 >= len(indexes):
	# 			continue
	# 		ans.append(indexes[i+2*K+1]-indexes[i])
	# if ans == []:
	# 	print(len(S))
	# else:
	# 	print(max(ans))