(define *memo* (make-hash-table))


(define (A k)
  (if (hash-table-exists? *memo* k)
    (hash-table-get *memo* k)
    (let ((val (cond ((= k 0) 4)
                     ((= k 1) 3)
                     (else (/ (- (* 19 (A (- k 1)))
                                 (* 12 (A (- k 2))))
                               4)))))
        (hash-table-put! *memo* k val)
        val)))


(let* ((k (read))
       (float (number->string (exact->inexact (A k))))
       (index (string-scan float #\e))
       (answer (if index (substring float 0 index) float)))
    (display answer)
    (newline))