public class LinkedStack<T> implements StackInterface<T> {

	private Node<T> topNode;

	public LinkedStack()
	{
		topNode = null;
	}


	@Override
	public boolean isEmpty() {
		// TODO Auto-generated method stub
		return topNode == null;
	}

	@Override
	public T pop() {

		T retVal = null;
		if(topNode  != null)
		{
			retVal = topNode.data;
			topNode = topNode.next;
		}
		return retVal;
	}

	@Override
	public void push(T entry) {
		Node<T> fresh = new Node<T>(entry, topNode);

		topNode = fresh;
	}

    /* Initializing the Node class */
    private class Node<T>
    {
        private T data;
        private Node<T> next;

        public Node(T data)
        {
            this.data = data;
            this.next = null;
        }

        public Node(T data, Node<T> next)
        {
            this.data = data;
            this.next = next;
        }
    }

	public static void main(String[] args)
	{
	char [] a = "5 9 8 + 4 6 * * 7 + *".toCharArray();
	//char [] a = "4 5 +";

	int N = a.length;

	LinkedStack<Integer> s = new LinkedStack<Integer>();
	for(int i=0; i< N; i++)
	{
		if(a[i] == '+')
			s.push(s.pop() + s.pop());
		if(a[i] == '-')
			s.push(s.pop() - s.pop() );
		if(a[i] == '*')
			s.push(s.pop() * s.pop());

		if(a[i] >= '0' && a[i] <= '9')
			s.push(0);
		while( (a[i] >= '0') && (a[i] <= '9') )
			s.push(10*s.pop() + (a[i++]-'0'));
	}
	System.out.println(s.pop()+ "   ");


}


}