; yukicoder My Practice
; author: Leonardone @ NEETSDKASU

(define n (read))

(define (c k) (integer->char (+ 65 k)))

(define (f r n)
	(if (< n 0) (list->string (map c r))
		(let ((a (remainder n 26)))
		     (f (cons a r) (- (quotient n 26) 1)))))

(display (f (list) n))
(newline)