;; Works with: chibi, csi, gosh, gsi, guile
(cond-expand
 (r7rs (import (scheme base)
               (scheme write)))
 (gambit)
 (chicken (import (r7rs))))

(define char-rot13
  (let* ((A (char->integer #\A))
         (N (char->integer #\N))
         (Z (char->integer #\Z))
         (a (char->integer #\a))
         (n (char->integer #\n))
         (z (char->integer #\z))
         (inc 13)
         (dec (- inc))
         (rot (lambda (c direction)
                (integer->char (+ c direction)))))
    (lambda (ch)
      (let ((c (char->integer ch)))
        (if (>= c A)
            (if (< c N)
                (rot c inc)
                (if (<= c Z)
                    (rot c dec)
                    (if (>= c a)
                        (if (< c n)
                            (rot c inc)
                            (if (<= c z)
                                (rot c dec)
                                ch))))))))))

(define (string-rot13 str)
  (string-map char-rot13 str))

(if (not (and (string=? (string-rot13 "abcdefghijklmnopqrstuvwxyz")
                        "nopqrstuvwxyzabcdefghijklm")
              (string=? (string-rot13 "ABCDEFGHIJKLMNOPQRSTUVWXYZ")
                        "NOPQRSTUVWXYZABCDEFGHIJKLM")))
    (error "Test failed."))

(let loop ((line (read-line)))
  (if (string? line)
      (begin
        (display (string-rot13 line))
        (newline)
        (loop (read-line)))))