class Aircraft {
	protected double speed, altitude;
	public void takeoff() {
		System.out.println("An aircraft is taking off");
	}
	public void fly() {
		System.out.println("An aircraft is flying");
	}
	public void land() {
		System.out.println("An aircraft is landing");
	}
}

class Airplane extends Aircraft {
	public void takeoff() {
		System.out.println("An airplane is taking off");
	}
	public void fly() {
		System.out.println("An airplane is flying");
	}
	public void land() {
		System.out.println("An airplane is landing");
	}
}

class Helicopter extends Aircraft {
	public void takeoff() {
		System.out.println("A helicopter is taking off");
	}
	public void fly() {
		System.out.println("A helicopter is flying");
	}
	public void land() {
		System.out.println("A helicopter is landing");
	}
}

class Blimp extends Aircraft {
	public void takeoff() {
		System.out.println("A blimp is taking off");
	}
	public void fly() {
		System.out.println("A blimp is flying");
	}
	public void land() {
		System.out.println("A blimp is landing");
	}
}