public Node getEntrance(Node head){
		if(head == null || head.next == null) return null;
		
		Node slow = head.next;
		Node fast = head.next.next;
		
		while(slow !=null && fast.next != null && fast != slow){
			slow = slow.next;
			fast = fast.next.next;
		}
		if(slow == null || fast.next == null)
			return null;
		
		Node r1 = head;
		Node r2 = fast;
		System.out.println("OK");
		while(r1 != r2){
			r1 = r1.next;
			r2 = r2.next;
		}
		return r1;		
	}