//SymNode is the node to contain the integer to be placed on stack
class SymNode {
    int value;
    SymNode next;

    public SymNode (int value, SymNode next) {
	this.value = value;
	this.next = next;
    }
}

//CStack is the dynamic stack (i.e. a linked list)
public class CStack {
    SymNode top; //Top keeps track of next element to pop
    
    //constructor just creates an empty stack
    public CStack () {
	top = null;
    }


    //Extra method to see if stack is empty - not necessary, but nice
    public boolean isEmpty () {
	return (top == null);
    }


    //push - should be saved on top of stack
    public void push (int value) {
	//creates a new node from an int value and set it
	//to top and to point to old top.
	top = new SymNode (value, top);
    }

    //pop - should return top and new top is node underneath
    public int pop () {
	int v = top.value;
	top = top.next;
	return v;
    }
}