n,k=map(int,input().split())
L=[int(i) for i in list(input())]

def t(x):
	a=b=0
	for i in range(x):
		if a>0:a-=1
		else:b+=1
		a+=L[i%n]
	return(b,b-a)

if k<n:y=t(k)[0]
else:
	if sum(L)>len(L):y=t(n)[0]
	else:y=t(n)[1]*(k//n)+t(k%n)[0]
	
print(y)