def linear_search(A, n, x):
	answer = None
	for i in range(n):
		if A[i] == x:
			answer = i
		else:
			continue
	return answer


def better_linear_search(A, n, x):
	answer = None
	for i in range(n):
		if A[i] == x:
			answer = i
			return answer
		else:
			continue
	return answer


def sentinel_linear_search(A, n, x):
	last = A[n-1]
	A[n-1] = x
	i = 0
	while A[i] != x:
		i++
	A[n] = last
	if i < n or A[n] == x:
		return i
	else:
		return None