interface Human {
  firstName: string;
  lastName: string;
}

class Person implements Human {
  constructor(public firstName, public lastName) {}

  name() {
    return `${this.firstName} ${this.lastName}`;
  }

  whoAreYou() {
    return `Hi i'm ${this.name()}`;
  }
}

class Student extends Person {
  course = '';

  constructor(firstName, lastName, course) {
    super(firstName, lastName);
    this.course = course;
  }

  whoAreYou() {
    return `${super.whoAreYou()} and i'm studying ${this.course}`;
  }
}

let Olha = new Person('Olha', 'Kurkaiedova');