public class Stack
    {
        List<object> stack;

        public Stack()
        {
            this.stack = new List<object>();
        }

        public void Push(object x)
        {
            stack.Add(x);
        }

        public object Pop()
        {
            if (this.IsEmpty())
                return "The stack is empty!!";
            object popped = stack[stack.Count-1];
            stack.RemoveAt(stack.Count-1);
            return popped;
        }

        public object Peek()
        {
            return stack[stack.Count-1];
        }

        public bool IsEmpty()
        {
            return (stack.Count == 0);
        }
    }