#| BEGIN (Write your solution here) |#
(define (f n) 
  (if (< n 3) n
      (+ (f (- n 1)) (* 2 (f (- n 2))) (* 3 (f (- n 3))))
  )
)

(define (f-iter n)
  (define (f-loop n current next further)
    (if (= n 0) current
        (f-loop (- n 1) next further (+ further (* 2 next) (* 3 current)))
    ))
  (f-loop n 0 1 2)
)
#| END |#