#include <iostream>
#include <ostream>

class Queue
{
public:
// We need to add the appropriate special member functions here
// It is also ok to add other function to this class

  void push(int value)
  {
    head = new Node {value, head};
  }
    
  void pop()
  {
    if ( head == nullptr )
    {
      throw std::runtime_error{"List Empty in pop()"};
    }
            
    Node** last{&head};
        
    while ((*last)->next != nullptr)
    {
      last = &(*last)->next;
    }
        
    delete *last;
    *last = nullptr;
  }

  int front() const
  {
    if ( head == nullptr )
    {
      throw std::runtime_error{"List Empty in front()"};
    }
            
    Node* last{head};
        
    while ( last->next != nullptr )
    {
      last = last->next;
    }
        
    return last->value;
  }
    
  bool empty() const
  {
    return head == nullptr;
  }

private:

  struct Node
  {
    int value;
    Node* next;
  };
  Node* head;
};