public class EdgeList
{
public EdgeLink head;
public EdgeLink tail;
    
public void add(int x1, int y1, int x2, int y2)
    {
	if(head==null)
	    {
		head = new EdgeLink(x1, y1, x2, y2);
		tail = head;
	    }
	else
	    {
		tail.next = new EdgeLink(x1, y1, x2, y2);
		tail = tail.next;
	    }
    }
}