N,K = map(int,raw_input().split())
S = raw_input()
need = [0]*(N+1)
luck = 0
for i in xrange(N):
	need[i+1] = need[i]
	if luck == 0:
		need[i+1] += 1
	else:
		luck -= 1
	luck += int(S[i])
if luck >= need[N]:
	print need[N]
else:
	m = K/N
	print need[K] if m < 1 else need[N]*m-luck*(m-1) + max(0,need[K%N]-luck)