type node struct {
 value interface{}
 prev *node
 next *node
}

type LinkedQueue struct {
 head *node
 tail *node
 size int
}

func (queue *LinkedQueue) Size() int {
 return queue.size
}

func (queue *LinkedQueue) Peek() interface{} {
 if queue.head == nil {
 panic("Empty queue.")
 }
 return queue.head.value
}

func (queue *LinkedQueue) Add(value interface{}) {
 new_node := &node{value, queue.tail, nil}
 if queue.tail == nil {
 queue.head = new_node
 queue.tail = new_node
 } else {
 queue.tail.next = new_node
 queue.tail = new_node
 }
 queue.size++
 new_node = nil
}

func (queue *LinkedQueue) Remove() {
 if queue.head == nil {
 panic("Empty queue.")
 }
 first_node := queue.head
 queue.head = first_node.next
 first_node.next = nil
 first_node.value = nil
 queue.size--
 first_node = nil
}