class Main {
  public static void main(String[] args) {
    DataSet ru = new DataSet();
    Person dan = new Person("Daniel",2.6);
    Person strick = new Person("Stricker",1.8);
    Person rick = new Person("Ricky",2.0);
    ru.add(dan);
    ru.add(strick);
    ru.add(rick);
    System.out.println(ru.getAverage());
  }
}

public class DataSet
{
  private double sum;
  private int nums;

  public void add (Measurable e)
  {
    sum = sum+e.getMeasure();
    nums++;
  }
  public double getAverage()
  {
    return sum/nums;
  }
}

public interface Measurable
{
  double getMeasure();
}

public class Person implements Measurable
{
  private String name;
  private double height;
  public Person (String n, double h)
  {
    name = n;
    height = h;
  }
  public double getMeasure()
  {
    return height;
  }
  public String getName()
  {
    return name;
  }
}