Buggy python submission (verdict: Runtime Error):
n, k = map(int, input().split())
s = list(map(lambda x: x == "1", list(input())))

change_flg = False
cnt = 0
ilands = []


def cumsum(array):
    value = array[0]
    results = [value] * len(array)
    for index, elm in enumerate(array[1:], 1):
        value += elm
        results[index] = value
    return results


def change():
    global cnt, change_flg
    ilands.append(cnt)
    cnt = 0
    change_flg = not change_flg

for value in s:
    if value: # case 1 cnt
        if change_flg:
            change()
    else: # case 0 cnt : plus
        if not change_flg:
            change()
    cnt += 1

ilands.append(cnt)

ilands += [0] * 10**5

if not len(ilands) % 2:
    ilands.append(0)

merged = list(cumsum(ilands))
section = 2 * k + 1

results = [0] * (len(ilands) // 2 - (k - 1))

merged.append(0)
for i in range(len(results)):
    start = i * 2 - 1
    results[i] = merged[start + section] - merged[start]

print(max(results))


Fixed submission:
n, k = map(int, input().split())
s = list(map(lambda x: x == "1", list(input())))

change_flg = False
cnt = 0
ilands = []


def cumsum(array):
    value = array[0]
    results = [value] * len(array)
    for index, elm in enumerate(array[1:], 1):
        value += elm
        results[index] = value
    return results


def change():
    global cnt, change_flg
    ilands.append(cnt)
    cnt = 0
    change_flg = not change_flg

for value in s:
    if value: # case 1 cnt
        if change_flg:
            change()
    else: # case 0 cnt : plus
        if not change_flg:
            change()
    cnt += 1

ilands.append(cnt)

if not len(ilands) % 2:
    ilands.append(0)

merged = list(cumsum(ilands))
section = 2 * k + 1

results = [0] * (len(ilands) // 2 - (k - 1))
if len(results) < 1 or len(merged) < section:
    print(n)
    exit()

merged.append(0)
for i in range(len(results)):
    start = i * 2 - 1
    results[i] = merged[start + section] - merged[start]

print(max(results))

Buggy python submission (verdict: Runtime Error):
n, k = map(int, input().split())
s = list(map(lambda x: x == "1", list(input())))

change_flg = False
cnt = 0
ilands = []


def cumsum(array):
    value = array[0]
    results = [value] * len(array)
    for index, elm in enumerate(array[1:], 1):
        value += elm
        results[index] = value
    return results


def change():
    global cnt, change_flg
    ilands.append(cnt)
    cnt = 0
    change_flg = not change_flg

for value in s:
    if value: # case 1 cnt
        if change_flg:
            change()
    else: # case 0 cnt : plus
        if not change_flg:
            change()
    cnt += 1

ilands.append(cnt)

if len(ilands) <= k:
    print(n)
    exit()

if not len(ilands) % 2:
    ilands.append(0)

merged = list(cumsum(ilands))
section = 2 * k + 1

results = [0] * (len(ilands) // 2 - (k - 1))

merged.append(0)
for i in range(len(results)):
    start = i * 2 - 1
    results[i] = merged[start + section] - merged[start]

print(max(results))


Fixed submission:
n, k = map(int, input().split())
s = list(map(lambda x: x == "1", list(input())))

change_flg = False
cnt = 0
ilands = []


def cumsum(array):
    value = array[0]
    results = [value] * len(array)
    for index, elm in enumerate(array[1:], 1):
        value += elm
        results[index] = value
    return results


def change():
    global cnt, change_flg
    ilands.append(cnt)
    cnt = 0
    change_flg = not change_flg

for value in s:
    if value: # case 1 cnt
        if change_flg:
            change()
    else: # case 0 cnt : plus
        if not change_flg:
            change()
    cnt += 1

ilands.append(cnt)

if not len(ilands) % 2:
    ilands.append(0)

merged = list(cumsum(ilands))
section = 2 * k + 1

results = [0] * (len(ilands) // 2 - (k - 1))
if len(results) < 1 or len(merged) < section:
    print(n)
    exit()

merged.append(0)
for i in range(len(results)):
    start = i * 2 - 1
    results[i] = merged[start + section] - merged[start]

print(max(results))

Buggy python submission (verdict: Runtime Error):
import numpy as np
n, k = map(int, input().split())
s = list(map(lambda x: x == "1", list(input())))


def p(value, *args, **kwargs):
    print(*map(int, value), *args, **kwargs)

# ---
change_flg = False
cnt = 0
ilands = []


def change():
    global cnt, change_flg
    ilands.append(cnt)
    cnt = 0
    change_flg = not change_flg

for value in s:
    if value: # case 1 cnt
        if change_flg:
            change()
    else: # case 0 cnt : plus
        if not change_flg:
            change()
    cnt += 1

ilands.append(cnt)

if len(ilands) <= k:
    print(n)
    exit()

if not len(ilands) % 2:
    ilands.append(0)

merged = list(np.cumsum(ilands))
section = 2 * k + 1

results = [0] * (len(ilands) // 2 - (k - 1))

merged.append(0)
for i in range(len(results)):
    start = i * 2 - 1
    results[i] = merged[start + section] - merged[start]
#     print(start, section + start, merged[section + start], merged[start])
# 
# print(ilands)
# print(merged)
# print(results, len(ilands) // 2 - (k - 1))

print(max(results))


Fixed submission:
n, k = map(int, input().split())
s = list(map(lambda x: x == "1", list(input())))

change_flg = False
cnt = 0
ilands = []


def cumsum(array):
    value = array[0]
    results = [value] * len(array)
    for index, elm in enumerate(array[1:], 1):
        value += elm
        results[index] = value
    return results


def change():
    global cnt, change_flg
    ilands.append(cnt)
    cnt = 0
    change_flg = not change_flg

for value in s:
    if value: # case 1 cnt
        if change_flg:
            change()
    else: # case 0 cnt : plus
        if not change_flg:
            change()
    cnt += 1

ilands.append(cnt)

if not len(ilands) % 2:
    ilands.append(0)

merged = list(cumsum(ilands))
section = 2 * k + 1

results = [0] * (len(ilands) // 2 - (k - 1))
if len(results) < 1 or len(merged) < section:
    print(n)
    exit()

merged.append(0)
for i in range(len(results)):
    start = i * 2 - 1
    results[i] = merged[start + section] - merged[start]

print(max(results))