public OurStack<T> Append(OurStack<T> otherStack)

        {

            Node pTmp = this.top;

            while (pTmp != null)

            {

                if (pTmp.Next == null) // if statment makes O(n+n)?

                {

                    Node mTmp = otherStack.top;

                    while (mTmp != null)

                    {

                        pTmp.Next = mTmp;

                        pTmp = pTmp.Next;

                        mTmp = mTmp.Next;

                    }

                    return this;

                }

                else

                {

                    pTmp = pTmp.Next;

                }

            }

            return this;

        }