public static void add2list(node n, node item, int index)
        {
            if (n == null || index < 0)
                return;
            if (index == 0)
            {
                node r = n.next;
                n.next = item;
                item.next = r;
                return;
            }
            add2list(n.next,item,index-1);
        }
 public class node
    {
        public node next { get; set; }
        public int value { get; set; }

        public node(int value ,node next)
        {
            this.next = next;
            this.value = value;

        }

    }