los(A)
	new vectors z1 and z2 = to A with all the values started at 1
	new var res = 1
	from i=1 to length(A) do:
		from j=0 to i do:
			if A[j] < A[i] and z1[i] < z2[j]+1:
				z1[i] = z2[j]+1
			if A[j] > A[i] and z2[i] < z1[i]+1:
				z2[i] = z1[j]+1


		if res < max(z1[i],z2[i])
			res = max(z1[i],z2[i])

	return res