def main0(n,k,s):
  cnt=0
  ans=0
  atari=0
  while cnt<k:
    for x in s:
      if atari:
        atari-=1
      else:
        ans+=1
      atari+=x
      cnt+=1
      if cnt==k:break
  return ans

def main1(n,k,s):
  cnt=0
  ans=0
  atari=0
  for x in s:
    if atari:
      atari-=1
    else:
      ans+=1
    atari+=x
    cnt+=1
    if cnt==k:return ans
  if atari>=ans:return ans
  d={}
  cnt=0
  ans=0
  atari=0
  while True:
    for i in range(n):
      x=s[i]
      if atari:
        atari-=1
      else:
        ans+=1
      atari+=x
      cnt+=1
      if cnt==k:return ans
      if (i,atari) in d:
        cnt0,ans0=d[(i,atari)]
        dcnt=cnt-cnt0
        dans=ans-ans0
        loopcnt=(k-cnt)//dcnt
        ans+=loopcnt*dans
        cnt+=loopcnt*dcnt
      else:
        d[(i,atari)]=cnt,ans

if __name__=='__main__':
  n,k=map(int,input().split())
  s=list(map(int,list(input())))
  #ret0=main0(n,k,s)
  ret1=main1(n,k,s)
  print(ret1)
  #print(ret0,ret1)