/**

 * Definition for singly-linked list.

 * public class ListNode {

 *     public int val;

 *     public ListNode next;

 *     public ListNode(int x) { val = x; }

 * }

 */

public class Solution {

    public ListNode OddEvenList(ListNode head) {

        if (head != null)

            {

                ListNode odd = head, even = head.next, evenHead = even;

                while (even != null && even.next != null)

                {

                    odd.next = odd.next.next;

                    even.next = even.next.next;

                    odd = odd.next;

                    even = even.next;

                }

                odd.next = evenHead;

            }

            return head;

    }

}

 class Solution:

     def oddEvenList(self, head: 'ListNode') -> 'ListNode':

         l = list()

         while head:

             l.append(head.val)

             head = head.next

         even = None

         odd = None

         temp = None

         if len(l) == :

             return None

         for i in range(len(l)-,-,-):

             if i %  == :

                 curodd = ListNode(l[i])

                 if not temp:

                     temp = curodd

                 curodd.next = odd

                 odd = curodd

             else:

                 cureven = ListNode(l[i])

                 cureven.next = even

                 even = cureven

         temp.next = even

         return odd

 class Solution:

     def oddEvenList(self, head: ListNode) -> ListNode:

         if head == None:

             return None

         odd,even,evenhead = head,head.next,head.next

         while even != None and even.next != None:

             odd.next = odd.next.next

             odd = odd.next

             even.next = even.next.next

             even = even.next

         odd.next = evenhead

         return head