n,A=map(int,input().split())
s=input()
x=s.count('0')
y=s.count('1')
a=[0]
b=[0]
for i in s:
	if i=='0':
		a.append(a[-1]+1)
		b.append(b[-1])
	else:
		a.append(a[-1])
		b.append(b[-1]+1)
ans=10**101
for i in range(n):
	if s[i]=='1':
		X=(A-a[i+1]+x-1)//x
		Y=(A-b[i+1]+y-1)//y
		t=max(X,Y)
		ans=min(ans,t*n+i+1)
print(ans)