import sys, bisect, math, itertools, string, queue, copy
# import numpy as np
# import scipy
from collections import Counter,defaultdict,deque
from itertools import permutations, combinations
from heapq import heappop, heappush
# input = sys.stdin.readline
sys.setrecursionlimit(10**8)
mod = 10**9+7
def inp(): return int(input()) # n=1
def inpm(): return map(int,input().split()) # x=1,y=2
def inpl(): return list(map(int, input().split())) # a=[1,2,3,4,5,...,n]
def inpls(): return list(input().split())  # a=['1','2','3',...,'n']
def inplm(n): return list(int(input()) for _ in range(n)) # x=[] 複数行
def inplL(n): return [list(input()) for _ in range(n)]
def inplT(n): return [tuple(input()) for _ in range(n)]
def inpll(n): return [list(map(int, input().split())) for _ in range(n)] # [[1,1,1,1],[2,2,2,2],[3,3,3,3]] 
def inplls(n): return sorted([list(map(int, input().split())) for _ in range(n)]) # [[1,1,1,1],[2,2,2,2],[3,3,3,3]] 
def graph():
    n=inp()
    g=[[] for _ in range(n)]
    for i in range(n):
        a = inp()
        a -= 1
        g[i].append(a)
        g[a].append(i)
    return n,g

def main():
    n,k = inpm()
    s = list(input())
    t = [0]
    for i in range(n-1):
        if s[i] != s[i+1]:
            t.append(i+1)
    a = len(t)
    for i in range(2*a+4):
        t.append(n)
    ans = 0
    if s[0]=='1':
        for i in range(a):
            ans = max(ans,t[2*k+2*i+1]-t[2*i])
    else:
        ans = t[2*k]
        for i in range(a):
            ans = max(ans,t[2*k+2*i+2]-t[2*i+1])
    print(ans)

if __name__ == "__main__":
    main()

### FIXED CODE ###

import sys, bisect, math, itertools, string, queue, copy
# import numpy as np
# import scipy
from collections import Counter,defaultdict,deque
from itertools import permutations, combinations
from heapq import heappop, heappush
# input = sys.stdin.readline
sys.setrecursionlimit(10**8)
mod = 10**9+7
def inp(): return int(input()) # n=1
def inpm(): return map(int,input().split()) # x=1,y=2
def inpl(): return list(map(int, input().split())) # a=[1,2,3,4,5,...,n]
def inpls(): return list(input().split())  # a=['1','2','3',...,'n']
def inplm(n): return list(int(input()) for _ in range(n)) # x=[] 複数行
def inplL(n): return [list(input()) for _ in range(n)]
def inplT(n): return [tuple(input()) for _ in range(n)]
def inpll(n): return [list(map(int, input().split())) for _ in range(n)] # [[1,1,1,1],[2,2,2,2],[3,3,3,3]] 
def inplls(n): return sorted([list(map(int, input().split())) for _ in range(n)]) # [[1,1,1,1],[2,2,2,2],[3,3,3,3]] 
def graph():
    n=inp()
    g=[[] for _ in range(n)]
    for i in range(n):
        a = inp()
        a -= 1
        g[i].append(a)
        g[a].append(i)
    return n,g

def main():
    n,k = inpm()
    s = list(input())
    t = [0]
    for i in range(n-1):
        if s[i] != s[i+1]:
            t.append(i+1)
    a = len(t)
    if len(t)<2*k-1:
        print(n)
        return
    for i in range(2*a+4):
        t.append(n)
    ans = 0
    if s[0]=='1':
        for i in range(a):
            if 2*k+2*i+1 >= len(t):
                break
            ans = max(ans,t[2*k+2*i+1]-t[2*i])
    else:
        ans = t[2*k]
        for i in range(a):
            if 2*k+2*i+2 >= len(t):
                break
            ans = max(ans,t[2*k+2*i+2]-t[2*i+1])
    print(ans)

if __name__ == "__main__":
    main()