n,k=map(int,input().split())
s=list(map(int,list(input())))
c=0;d=0;
for i in s:
    if d:
        d-=1;d+=i
    else:
        c+=1;d+=i
    if c+d>=k:
        print(c);exit()
k-=n
if d>=c:
    print(c)
else:
    ans=c+(k//n*(c-d))
    k%=n
    for i in s:
        if k==0:
            break
        if d:
            d-=1
        else:
            ans+=1
        d+=i;k-=1
    print(ans)