n,k=map(int,input().split())
s=input()
m=min([max(s.find(c),0) for c in "12"])+1

u=len(s)-sum(map(int,s))

if u<0:
    ans=min(m,k)
else:
    ans=k//n*u
    ans+=min(m,k%n)

print(ans)