import sys
input=lambda:sys.stdin.readline().rstrip()
N,K=map(int,input().split())
S=list(map(int,list(input())))
mid=max((K-1)//N-1,0)
ans,rem=mid*max(N-sum(S),0),0
for i in range(K-mid*N):
	ans+=(rem==0)
	rem+=S[i%N]-(rem>0)
print(ans)