abstract class Firkant 
{
    protected int a;
    protected int b;
    protected int c;
    protected int d;

    public Firkant(int a, int b, int c, int d)
    {
        this.a = a;
        this.b = b;
        this.c = c;
        this.d = d;
    }

    public int omkrets()
    {
        return a+b+c+d;
    }

    // M? implementers i subklasser.
    public abstract int areal();

    @Override
    public String toString()
    {
        return String.format(" med areal: %s  Omkrets: %s", areal(), omkrets());
    }
}