public static ListNode removeNthFromEnd(ListNode head, int n) {
        ListNode runner1=head,runner2=head;
        
        for(int i=0;i<n;i++) runner2=runner2.next;

        if(runner2==null)return head.next;
        
        while(runner2.next !=null){
            runner2=runner2.next;
            runner1=runner1.next;
        }
        
        runner1.next=runner1.next.next;
        
        return head;
        
    }