Buggy python submission (verdict: Runtime Error):
N, K = map(int,input().split(' '))
S = input()
S2=[]
key=S[0]
tmpcnt=1
if key=='0':
    S2.append(0)
for i in range(1,len(S)):
    if key!=S[i]:
        if key == '0':
            S2.append(-1*tmpcnt)
        else:
            S2.append(tmpcnt)
        key=S[i]
        tmpcnt=1
    else:
        tmpcnt+=1
if key == '0':
    S2.append(-1*tmpcnt)
    S2.append(0)
    S2.append(0)
else:
    S2.append(tmpcnt)
    S2.append(0)
    S2.append(0)
#print(S2)
max=0
tmp=S2[i]
maxj=len(S2)-1
for j in range(1,K*2+1):
    tmp+=abs(S2[min(0+j,maxj)])
    #print(S2[i],S2[min(i+j,maxj)])
if tmp >= max:
    max=tmp
    #print(tmp)

for i in range(2,len(S2)):
    tmp-=abs(S[i-1])
    tmp-=abs(S[i-2])
    tmp+=abs(S[min(i+j,maxj)])
    tmp+=abs(S[min(i+j+1,maxj)])
    if tmp>= max:
        max=tmp
print(max)


Fixed submission:
N, K = map(int,input().split(' '))
S = input()
S2=[]
key=S[0]
tmpcnt=1
if key=='0':
    S2.append(0)
S2.append(0)
S2.append(0)
for i in range(1,len(S)):
    if key!=S[i]:
        if key == '0':
            S2.append(-1*tmpcnt)
        else:
            S2.append(tmpcnt)
        key=S[i]
        tmpcnt=1
    else:
        tmpcnt+=1
if key == '0':
    S2.append(-1*tmpcnt)
    S2.append(0)
    S2.append(0)
else:
    S2.append(tmpcnt)
    S2.append(0)
    S2.append(0)
#print(S2)
max=0
tmp=S2[0]
maxj=len(S2)-1
for j in range(1,K*2+1):
    tmp+=abs(S2[min(0+j,maxj)])
    #print(S2[i],S2[min(i+j,maxj)])
if tmp >= max:
    max=tmp
    #print(tmp)

for i in range(2,len(S2),2):
    tmp-=abs(S2[i-1])
    tmp-=abs(S2[i-2])
    tmp+=abs(S2[min(i+j-1,maxj)])
    tmp+=abs(S2[min(i+j,maxj)])
    #print(i-1,i-2,i+j-1,i+j)
    #print(tmp)
    if tmp>= max:
        max=tmp
print(max)

Buggy python submission (verdict: Time Limit Exceeded):
N, K = map(int,input().split(' '))
S = input()
S2=[]
key=S[0]
tmpcnt=1
if key=='0':
    S2.append(0)
for i in range(1,len(S)):
    if key!=S[i]:
        if key == '0':
            S2.append(-1*tmpcnt)
        else:
            S2.append(tmpcnt)
        key=S[i]
        tmpcnt=1
    else:
        tmpcnt+=1
if key == '0':
    S2.append(-1*tmpcnt)
    S2.append(0)
    S2.append(0)
else:
    S2.append(tmpcnt)
    S2.append(0)
    S2.append(0)
#print(S2)
max=0
for i in range(0,len(S2),2):
    tmp=S2[i]
    maxj=len(S2)-1
    for j in range(1,K*2+1):
        tmp+=abs(S2[min(i+j,maxj)])
        #print(S2[i],S2[min(i+j,maxj)])
    if tmp >= max:
        max=tmp
    #print(tmp)
print(max)

Fixed submission:
N, K = map(int,input().split(' '))
S = input()
S2=[]
key=S[0]
tmpcnt=1
if key=='0':
    S2.append(0)
S2.append(0)
S2.append(0)
for i in range(1,len(S)):
    if key!=S[i]:
        if key == '0':
            S2.append(-1*tmpcnt)
        else:
            S2.append(tmpcnt)
        key=S[i]
        tmpcnt=1
    else:
        tmpcnt+=1
if key == '0':
    S2.append(-1*tmpcnt)
    S2.append(0)
    S2.append(0)
else:
    S2.append(tmpcnt)
    S2.append(0)
    S2.append(0)
#print(S2)
max=0
tmp=S2[0]
maxj=len(S2)-1
for j in range(1,K*2+1):
    tmp+=abs(S2[min(0+j,maxj)])
    #print(S2[i],S2[min(i+j,maxj)])
if tmp >= max:
    max=tmp
    #print(tmp)

for i in range(2,len(S2),2):
    tmp-=abs(S2[i-1])
    tmp-=abs(S2[i-2])
    tmp+=abs(S2[min(i+j-1,maxj)])
    tmp+=abs(S2[min(i+j,maxj)])
    #print(i-1,i-2,i+j-1,i+j)
    #print(tmp)
    if tmp>= max:
        max=tmp
print(max)