if(root==NULL)return NULL;
    if(root->next==NULL)return root;
    Node* after=NULL;
    Node* prev=NULL;
    
    after=root->next->next;
    prev=root->next;
    root->next->next=root;
    root->next=NULL;
    while(after!=NULL)
    {
        Node* temp=after->next;
        after->next=prev;
        prev=after;
        after=temp;
    }
    return prev;