class stack1
    {
       public int[] _array;
 
        private const int defaultCapacity = 1;
        private int size;
        public stack1()
        {
            this.size = 0;
            this._array = new int[defaultCapacity];
        }
        public bool IsEmpty()
        {
            return this.size == 0;
        }
        public virtual int Count
        {
            get { return this.size; }
        }
        public int Pop()
        {
            if (this.size == 0)
                throw new InvalidOperationException();
            return this._array[--this.size];
        }
        public void Push(int newElement)
        {
            if (this.size == this._array.Length)
            {
                int[] newArray = new int[2 * this._array.Length];
                Array.Copy(this._array, 0, newArray, 0, this.size);
                this._array = newArray;
            }
            this._array[this.size++] = newElement;
        }
    }

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