def do_OP_TUCK(stack):
    """
    >>> s = [1, 2, 3]
    >>> do_OP_TUCK(s)
    >>> print(s)
    [1, 3, 2, 3]
    """
    v1 = stack.pop()
    v2 = stack.pop()
    stack.append(v1)
    stack.append(v2)
    stack.append(v1)
