#include <iostream>

using namespace std;

class Set {
 private:
  // implementation details:
  // ...
  int a;
 public:
  // public interface:
  Set(); // the default constructor 
         //  - initializes the set to empty set
  Set(long a, long b, long c=1); // initializes the set to the set
    // containing the elements a, a+c, a+2*c, a+3*c, ...
    // which are smaller or equal to b
  Set(long list[],long size); // initializes the set to elements
    // contained in the array list; the size should be size of the array
    // (note: you cannot assume that elements in list are all distinct)
  Set(const Set &s); // the copy constructor
  ~Set(); // destructor

  // if the following methods return a reference to Set, 
  // it should be reference to itself (which allows chaining of the operations)
  Set & operator=(const Set &s); // the assignment operator
  operator long() const; // return the number of elements
  bool operator()(long x) const; // return true if x is an element of the set
  bool operator==(const Set &s) const; 
    // return true if s contains the same elements
  bool operator<=(const Set &s) const;
    // return true if this object is subset of s
  bool operator>=(const Set &s) const;
    // return true if s is subset of this object

  Set & operator<<(long x); // add x to the set
  Set & operator>>(long x); // remove x from the set
    // (if x is not in the set, do nothing)
  Set operator+(const Set &s) const; // return the union with the set s
  Set & operator+=(const Set &s); // add all elements of the set s
  Set operator*(const Set &s) const; // return the intersection with the set s
  Set & operator*=(const Set &s);
    // keep only those elements which are also in s
  Set operator-(const Set &s) const; // return the set difference with the set s
  Set & operator-=(const Set &s); // remove those elements which are also in s
  friend ostream & operator<<(ostream &os, const Set &s);
    // print the content of the set s
};