/** A WeirdList holds a sequence of integers. */
public class WeirdList {
    /** The empty sequence of integers. */
    public static WeirdList EMPTY = 
        null;  // REPLACE THIS LINE WITH THE RIGHT ANSWER.
   
    /** A new WeirdList whose head is HEAD and tail is 
     *  TAIL. */
    public WeirdList (int head, WeirdList tail) { /* FILL IN */ }

    /** The number of elements in the sequence that
     *  starts with THIS. */
    public int length () { 
        return 0;  // REPLACE THIS LINE WITH THE RIGHT ANSWER.
    }

    /** Apply func.apply to every element of THIS WeirdList in
     *  sequence, and return a WeirdList of the resulting values. */
    public WeirdList map (IntUnaryFunction x) { 
        return null;  // REPLACE THIS LINE WITH THE RIGHT ANSWER.
    }

    /** Print the contents of THIS WeirdList on the standard output
     *  (on one line, each followed by a blank).  Does not print
     *  an end-of-line. */
    public void print () { /* FILL IN */ }

    // FILL IN WITH *PRIVATE* FIELDS ONLY.
    // You should NOT need any more methods here.
}

// FILL IN OTHER CLASSES HERE (HINT, HINT).

class User {
    /** The result of adding N to each element of L. */    
    static WeirdList add (WeirdList L, int n) { 
        return null; // REPLACE THIS LINE WITH THE RIGHT ANSWER.
    }
   
    /** The sum of the elements in L */
    static int sum (WeirdList L) { 
        return 0; // REPLACE THIS LINE WITH THE RIGHT ANSWER.
    }
}