func mergeTwoLists(l1 *ListNode, l2 *ListNode) *ListNode {
	result := &ListNode{Val: -1 << 63}
	tail := result
	for l1 != nil && l2 != nil {
		if l1.Val < l2.Val {
			tail.Next = l1
			l1 = l1.Next
		} else {
			tail.Next = l2
			l2 = l2.Next
		}
		tail = tail.Next
	}
	if l1 != nil {
		tail.Next = l1
	}

	if l2 != nil {
		tail.Next = l2
	}
	return result.Next
}