// -- Node struct (for elements of the linked list)
struct Node
{
 string value;
 Node * next;
};

// -- Main Queue class
class Queue
{
private:
 Node * front;
 Node * back;
public:

 // -- Add an element to the back
 void add(string s);

 // -- Remove an element from the front
 string remove();

 // -- Return true if the queue is empty
 bool empty() { return ((front == NULL) && (back == NULL)); }
};

void Queue::add(string s)
{
 Node * n = new Node();
 n->value = s;
 if (empty()) {
   front = n;
   back = n;
 } else {
   back->next = n;
   back = n;
 }
}

string Queue::remove()
{
 if ( ! empty()) {
   Node * temp = front;
   string result = temp->value;
   delete temp;
   front = front->next;
   return result;
 }
 return "";
}