class Stack
{

	private int size;
	private Object[] data;
	private int count;

	Stack(int size)
	{
		this.size = size;
		this.data = new Object[this.size];
		this.count = 0;
	}

	public void synchronized push(Object value)
	{
		if(count >= size)
		{
			throw new OverflowStackException("Overflow " + count + "/" + size);
		}
		data[count++] = value;
	}

	public Object top()
	{
		if(count <= 0)
		{
			throw new EmptyStackException("Empty " + count + "/" + size);
		}
		return data[count - 1];
	}

	public void synchronized pop()
	{
		if(count <= 0)
		{
			throw new EmptyStackException("Empty " + count + "/" + size);
		}
		data[--count] = null;
	}

	public boolean isEmpty()
	{
		return (count <= 0);
	}

	public boolean isFull()
	{
		return (count >= size);
	}

	public void synchronized clear()
	{
		for(int i = (count - 1);i >= 0;i--)
		{
			data[i] = null;
			count = 0;
		}
	}
}

interface StackException extends Exception
{

}

class EmptyStackException implements StackException
{

}

class OverflowStackException implements StackException
{

}