def stairs(n):
    """Give the number of ways to take n steps, given that at each step, you
    can choose to take 1, 2, or 3 steps.

    >>> stairs(3)
    4
    >>> stairs(5)
    13
    >>> stairs(10)
    274
    """
    if n <= 2:
        return n
    if n == 3:
        return 4
    return stairs(n-1) + stairs(n-2) + stairs(n-3)