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])
m = K/N
if m < 1:
	print need[K]	
else:
	print need[N] if luck >= need[N] else need[N]*m-luck*(m-1) + max(0,need[K%N]-luck)