loop

	public ListNode findStart(ListNode head){
		ListNode slow = head;
		ListNode fast = head;
		while(fast != null && fast.next != null){
			slow = slow.next;
			fast = fast.next.next;
			if(slow == fast)
				break;
		}
		
		if(fast == null || fast.next == null)
			return null;
		
		slow = head;
		while(slow != fast){
			slow = slow.next;
			fast = fast.next;
		}
		return fast;
	}