//A stack is a structure that allows you to add and remove
//elements from it, where the last in is the first out.  
//That is, if you add 'a', then 'b', then the next time you 
//remove an element, it must be 'b'.
public class Stack {
	//Data member.
	LinkedList list;
	int count;
	
	public Stack()
	{
		list = new LinkedList();
		count = 0;
	}
	
	//push something onto the stack.
	public void push(int n)
	{
		list.insert(n);
		count++;
		
	}
	
	//take an item off the top of the stack and remove it.
	public int pop()
	{
		int res = list.getVal(0);
		list.remove(0);
		count--;
		return res;
	}
	
	//return the item on the top off the stack.
	public int peek()
	{
		return list.getVal(0);
	}
	
	public int size()
	{
		//return list.length();
		return count;
	}
}