public ListNode swapPairs(ListNode head) {
	 if(head==null)return head;
	 ListNode value=new ListNode(0);
	 value.next=head;
	 ListNode team=value;
	 ListNode first;
	 ListNode second;
	 while (team!=null&&team.next!=null) {
		if(team.next.next==null)
			return value.next;
		first=team.next;
	    second=team.next.next;
		
	    team.next=second;
	    first.next=second.next;
	    second.next=first;
	    
		team=first;//team=team.next.next
	}
	 return value.next;
 }