def is_list_palindrome(lst):
    start = 0
    end = len(lst) - 1
    while start < end:
        if lst[start] != lst[end]:
            print("The list is not a palindrome.")
            return
        start += 1
        end -= 1
    print("The list is a palindrome.")

# Example usage
is_list_palindrome([1, 2, 3, 2, 1])
is_list_palindrome([1, 2, 3])

The list is a palindrome.
The list is not a palindrome.