public class Krog{
	protected double r;
	
	public Krog (double r){
		this.r = r;
	}
	
	public double premer(){
		return 2*r;
	}
	
	public double obseg(){
		return 2*Math.PI*r;
	}
	
	public double kvadratura(){
		return Math.PI*r*r;
	}
}