class Person {
  String name;
  Integer birthYear;
  Person(String name, int birth){
    this.name = name;
    birthYear = birth;          // boxing
  }
  Integer age(){
    return 2004-birthYear;      // unboxing & boxing
  }
}

class Student extends Person{
  String university;
  Student(String name, int birth){
    super(name, birth);
    university = "Copenhagen";
  }
  Student(String name, int birth, String university){
    super(name, birth);
    this.university = university;
  }
}