import java.util.*;

public class EV
{
    public static Integer ev (E e, Map <String, Integer> env) { throw new RuntimeException ("oops: " + e); }
    public static Integer ev (V e, Map <String, Integer> env) { return env.get (e.name); }
    public static Integer ev (C e, Map <String, Integer> env) { return e.value; }
    public static Integer ev (P e, Map <String, Integer> env) { return ev (e.a1, env) + ev (e.a2, env); }
    public static Integer ev (T e, Map <String, Integer> env) { return ev (e.a1, env) * ev (e.a2, env); }

    public static void main (String [] a)
    {
        E e = new P (new T (new C (2), new V ("a")), new V ("b"));
        Map <String, Integer> env = new Hashtable <String, Integer> ();
        env.put ("a", 123);
        env.put ("b", 456);
        System.out.println ("ev (e, env) => " + ev (e, env));
    }
}

class E {}

class V extends E
{
    String name;
    public V (String name) { this.name = name; }
}

class C extends E
{
    Integer value;
    public C (Integer value) { this.value = value; }
}

class P extends E
{
    E a1, a2;
    public P (E a1, E a2) { this.a1 = a1; this.a2 = a2; }
}

class T extends E
{
    E a1, a2;
    public T (E a1, E a2) { this.a1 = a1; this.a2 = a2; }
}