code: def swap_pairs(head):
      if not head:
          return head
      start = Node(0)
      start.next = head
      current = start
      while current.next and current.next.next:
          first = current.next
          second = current.next.next
          first.next = second.next
          current.next = second
          current.next.next = first
          current = current.next.next
      return start.next
  
label_desc: Use image node_id 1 for calling a global function with example usage: swap_pairs(head) and returns: start, head