Problem:
Score : 400 points

Problem Statement

N people are arranged in a row from left to right.

You are given a string S of length N consisting of 0 and 1, and a positive integer K.

The i-th person from the left is standing on feet if the i-th character of S is 0, and standing on hands if that character is 1.

You will give the following direction at most K times (possibly zero):

Direction: Choose integers l and r satisfying 1 \leq l \leq r \leq N, and flip the l-th, (l+1)-th, ..., and r-th persons. That is, for each i = l, l+1, ..., r, the i-th person from the left now stands on hands if he/she was standing on feet, and stands on feet if he/she was standing on hands.

Find the maximum possible number of consecutive people standing on hands after at most K directions.

Constraints

N is an integer satisfying 1 \leq N \leq 10^5.

K is an integer satisfying 1 \leq K \leq 10^5.

The length of the string S is N.

Each character of the string S is 0 or 1.

Input

Input is given from Standard Input in the following format:

N K
S

Output

Print the maximum possible number of consecutive people standing on hands after at most K directions.

Sample Input 1

5 1
00010

Sample Output 1

4

We can have four consecutive people standing on hands, which is the maximum result, by giving the following direction:

Give the direction with l = 1, r = 3, which flips the first, second and third persons from the left.

Sample Input 2

14 2
11101010110011

Sample Output 2

8

Sample Input 3

1 1
1

Sample Output 3

1

No directions are necessary.

Solution in Python (3.4.3) (judge verdict: Accepted)

#D
from collections import deque
n,k=map(int,input().split())
s=input()
if n==1:
    print(1)
elif "1" not in s:
  	print(len(s))
else:
    a=deque([])
    if s[0]=="1":
        a.append([0])
    for i in range(1,n):
        if s[i-1:i+1]=="01":
            a.append([i])
        elif s[i-1:i+1]=="10":
            a[-1].append(i-1)
    if s[n-1]=="1":
        a[-1].append(n-1)
    if a[0][0]!=0:
        a.appendleft([0,0])
    if a[-1][1]!=n-1:
        a.append([n-1,n-1])
    if len(a)-1<=k:
        print(n)
    else:
        t=0
        for i in range(len(a)-k):
            t=max(t,a[i+k][1]-a[i][0]+1)
        print(t)